diff --git a/homeassistant/components/adguard/sensor.py b/homeassistant/components/adguard/sensor.py
index 9d0d5245d80..5abff10739a 100644
--- a/homeassistant/components/adguard/sensor.py
+++ b/homeassistant/components/adguard/sensor.py
@@ -11,7 +11,7 @@ from homeassistant.components.adguard.const import (
     DOMAIN,
 )
 from homeassistant.config_entries import ConfigEntry
-from homeassistant.const import TIME_MILLISECONDS
+from homeassistant.const import TIME_MILLISECONDS, UNIT_PERCENTAGE
 from homeassistant.exceptions import PlatformNotReady
 from homeassistant.helpers.typing import HomeAssistantType
 
@@ -134,7 +134,7 @@ class AdGuardHomePercentageBlockedSensor(AdGuardHomeSensor):
             "AdGuard DNS Queries Blocked Ratio",
             "mdi:magnify-close",
             "blocked_percentage",
-            "%",
+            UNIT_PERCENTAGE,
         )
 
     async def _adguard_update(self) -> None:
diff --git a/homeassistant/components/airly/sensor.py b/homeassistant/components/airly/sensor.py
index 2d42dac5614..a6754b4a00d 100644
--- a/homeassistant/components/airly/sensor.py
+++ b/homeassistant/components/airly/sensor.py
@@ -9,6 +9,7 @@ from homeassistant.const import (
     DEVICE_CLASS_TEMPERATURE,
     PRESSURE_HPA,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.entity import Entity
 
@@ -27,8 +28,6 @@ ATTR_ICON = "icon"
 ATTR_LABEL = "label"
 ATTR_UNIT = "unit"
 
-HUMI_PERCENT = "%"
-
 SENSOR_TYPES = {
     ATTR_API_PM1: {
         ATTR_DEVICE_CLASS: None,
@@ -40,7 +39,7 @@ SENSOR_TYPES = {
         ATTR_DEVICE_CLASS: DEVICE_CLASS_HUMIDITY,
         ATTR_ICON: None,
         ATTR_LABEL: ATTR_API_HUMIDITY.capitalize(),
-        ATTR_UNIT: HUMI_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_API_PRESSURE: {
         ATTR_DEVICE_CLASS: DEVICE_CLASS_PRESSURE,
diff --git a/homeassistant/components/ambient_station/__init__.py b/homeassistant/components/ambient_station/__init__.py
index 63c00b05038..4fd6590b286 100644
--- a/homeassistant/components/ambient_station/__init__.py
+++ b/homeassistant/components/ambient_station/__init__.py
@@ -14,6 +14,7 @@ from homeassistant.const import (
     CONF_API_KEY,
     EVENT_HOMEASSISTANT_STOP,
     SPEED_MILES_PER_HOUR,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import callback
 from homeassistant.exceptions import ConfigEntryNotReady
@@ -154,18 +155,18 @@ SENSOR_TYPES = {
     TYPE_EVENTRAININ: ("Event Rain", "in", TYPE_SENSOR, None),
     TYPE_FEELSLIKE: ("Feels Like", "°F", TYPE_SENSOR, "temperature"),
     TYPE_HOURLYRAININ: ("Hourly Rain Rate", "in/hr", TYPE_SENSOR, None),
-    TYPE_HUMIDITY10: ("Humidity 10", "%", TYPE_SENSOR, "humidity"),
-    TYPE_HUMIDITY1: ("Humidity 1", "%", TYPE_SENSOR, "humidity"),
-    TYPE_HUMIDITY2: ("Humidity 2", "%", TYPE_SENSOR, "humidity"),
-    TYPE_HUMIDITY3: ("Humidity 3", "%", TYPE_SENSOR, "humidity"),
-    TYPE_HUMIDITY4: ("Humidity 4", "%", TYPE_SENSOR, "humidity"),
-    TYPE_HUMIDITY5: ("Humidity 5", "%", TYPE_SENSOR, "humidity"),
-    TYPE_HUMIDITY6: ("Humidity 6", "%", TYPE_SENSOR, "humidity"),
-    TYPE_HUMIDITY7: ("Humidity 7", "%", TYPE_SENSOR, "humidity"),
-    TYPE_HUMIDITY8: ("Humidity 8", "%", TYPE_SENSOR, "humidity"),
-    TYPE_HUMIDITY9: ("Humidity 9", "%", TYPE_SENSOR, "humidity"),
-    TYPE_HUMIDITY: ("Humidity", "%", TYPE_SENSOR, "humidity"),
-    TYPE_HUMIDITYIN: ("Humidity In", "%", TYPE_SENSOR, "humidity"),
+    TYPE_HUMIDITY10: ("Humidity 10", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_HUMIDITY1: ("Humidity 1", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_HUMIDITY2: ("Humidity 2", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_HUMIDITY3: ("Humidity 3", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_HUMIDITY4: ("Humidity 4", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_HUMIDITY5: ("Humidity 5", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_HUMIDITY6: ("Humidity 6", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_HUMIDITY7: ("Humidity 7", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_HUMIDITY8: ("Humidity 8", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_HUMIDITY9: ("Humidity 9", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_HUMIDITY: ("Humidity", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_HUMIDITYIN: ("Humidity In", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
     TYPE_LASTRAIN: ("Last Rain", None, TYPE_SENSOR, "timestamp"),
     TYPE_MAXDAILYGUST: ("Max Gust", SPEED_MILES_PER_HOUR, TYPE_SENSOR, None),
     TYPE_MONTHLYRAININ: ("Monthly Rain", "in", TYPE_SENSOR, None),
@@ -179,16 +180,16 @@ SENSOR_TYPES = {
     TYPE_RELAY7: ("Relay 7", None, TYPE_BINARY_SENSOR, "connectivity"),
     TYPE_RELAY8: ("Relay 8", None, TYPE_BINARY_SENSOR, "connectivity"),
     TYPE_RELAY9: ("Relay 9", None, TYPE_BINARY_SENSOR, "connectivity"),
-    TYPE_SOILHUM10: ("Soil Humidity 10", "%", TYPE_SENSOR, "humidity"),
-    TYPE_SOILHUM1: ("Soil Humidity 1", "%", TYPE_SENSOR, "humidity"),
-    TYPE_SOILHUM2: ("Soil Humidity 2", "%", TYPE_SENSOR, "humidity"),
-    TYPE_SOILHUM3: ("Soil Humidity 3", "%", TYPE_SENSOR, "humidity"),
-    TYPE_SOILHUM4: ("Soil Humidity 4", "%", TYPE_SENSOR, "humidity"),
-    TYPE_SOILHUM5: ("Soil Humidity 5", "%", TYPE_SENSOR, "humidity"),
-    TYPE_SOILHUM6: ("Soil Humidity 6", "%", TYPE_SENSOR, "humidity"),
-    TYPE_SOILHUM7: ("Soil Humidity 7", "%", TYPE_SENSOR, "humidity"),
-    TYPE_SOILHUM8: ("Soil Humidity 8", "%", TYPE_SENSOR, "humidity"),
-    TYPE_SOILHUM9: ("Soil Humidity 9", "%", TYPE_SENSOR, "humidity"),
+    TYPE_SOILHUM10: ("Soil Humidity 10", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_SOILHUM1: ("Soil Humidity 1", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_SOILHUM2: ("Soil Humidity 2", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_SOILHUM3: ("Soil Humidity 3", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_SOILHUM4: ("Soil Humidity 4", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_SOILHUM5: ("Soil Humidity 5", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_SOILHUM6: ("Soil Humidity 6", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_SOILHUM7: ("Soil Humidity 7", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_SOILHUM8: ("Soil Humidity 8", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
+    TYPE_SOILHUM9: ("Soil Humidity 9", UNIT_PERCENTAGE, TYPE_SENSOR, "humidity"),
     TYPE_SOILTEMP10F: ("Soil Temp 10", "°F", TYPE_SENSOR, "temperature"),
     TYPE_SOILTEMP1F: ("Soil Temp 1", "°F", TYPE_SENSOR, "temperature"),
     TYPE_SOILTEMP2F: ("Soil Temp 2", "°F", TYPE_SENSOR, "temperature"),
diff --git a/homeassistant/components/amcrest/sensor.py b/homeassistant/components/amcrest/sensor.py
index bcff1775879..18abf28bdd5 100644
--- a/homeassistant/components/amcrest/sensor.py
+++ b/homeassistant/components/amcrest/sensor.py
@@ -4,7 +4,7 @@ import logging
 
 from amcrest import AmcrestError
 
-from homeassistant.const import CONF_NAME, CONF_SENSORS
+from homeassistant.const import CONF_NAME, CONF_SENSORS, UNIT_PERCENTAGE
 from homeassistant.helpers.dispatcher import async_dispatcher_connect
 from homeassistant.helpers.entity import Entity
 
@@ -20,7 +20,7 @@ SENSOR_SDCARD = "sdcard"
 # Sensor types are defined like: Name, units, icon
 SENSORS = {
     SENSOR_PTZ_PRESET: ["PTZ Preset", None, "mdi:camera-iris"],
-    SENSOR_SDCARD: ["SD Used", "%", "mdi:sd"],
+    SENSOR_SDCARD: ["SD Used", UNIT_PERCENTAGE, "mdi:sd"],
 }
 
 
diff --git a/homeassistant/components/apcupsd/sensor.py b/homeassistant/components/apcupsd/sensor.py
index 7947ba75999..e39696cc37a 100644
--- a/homeassistant/components/apcupsd/sensor.py
+++ b/homeassistant/components/apcupsd/sensor.py
@@ -12,6 +12,7 @@ from homeassistant.const import (
     TEMP_CELSIUS,
     TIME_MINUTES,
     TIME_SECONDS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -28,7 +29,7 @@ SENSOR_TYPES = {
     "battdate": ["Battery Replaced", "", "mdi:calendar-clock"],
     "battstat": ["Battery Status", "", "mdi:information-outline"],
     "battv": ["Battery Voltage", "V", "mdi:flash"],
-    "bcharge": ["Battery", "%", "mdi:battery"],
+    "bcharge": ["Battery", UNIT_PERCENTAGE, "mdi:battery"],
     "cable": ["Cable Type", "", "mdi:ethernet-cable"],
     "cumonbatt": ["Total Time on Battery", "", "mdi:timer"],
     "date": ["Status Date", "", "mdi:calendar-clock"],
@@ -42,20 +43,20 @@ SENSOR_TYPES = {
     "firmware": ["Firmware Version", "", "mdi:information-outline"],
     "hitrans": ["Transfer High", "V", "mdi:flash"],
     "hostname": ["Hostname", "", "mdi:information-outline"],
-    "humidity": ["Ambient Humidity", "%", "mdi:water-percent"],
+    "humidity": ["Ambient Humidity", UNIT_PERCENTAGE, "mdi:water-percent"],
     "itemp": ["Internal Temperature", TEMP_CELSIUS, "mdi:thermometer"],
     "lastxfer": ["Last Transfer", "", "mdi:transfer"],
     "linefail": ["Input Voltage Status", "", "mdi:information-outline"],
     "linefreq": ["Line Frequency", "Hz", "mdi:information-outline"],
     "linev": ["Input Voltage", "V", "mdi:flash"],
-    "loadpct": ["Load", "%", "mdi:gauge"],
-    "loadapnt": ["Load Apparent Power", "%", "mdi:gauge"],
+    "loadpct": ["Load", UNIT_PERCENTAGE, "mdi:gauge"],
+    "loadapnt": ["Load Apparent Power", UNIT_PERCENTAGE, "mdi:gauge"],
     "lotrans": ["Transfer Low", "V", "mdi:flash"],
     "mandate": ["Manufacture Date", "", "mdi:calendar"],
     "masterupd": ["Master Update", "", "mdi:information-outline"],
     "maxlinev": ["Input Voltage High", "V", "mdi:flash"],
     "maxtime": ["Battery Timeout", "", "mdi:timer-off"],
-    "mbattchg": ["Battery Shutdown", "%", "mdi:battery-alert"],
+    "mbattchg": ["Battery Shutdown", UNIT_PERCENTAGE, "mdi:battery-alert"],
     "minlinev": ["Input Voltage Low", "V", "mdi:flash"],
     "mintimel": ["Shutdown Time", "", "mdi:timer"],
     "model": ["Model", "", "mdi:information-outline"],
@@ -70,7 +71,7 @@ SENSOR_TYPES = {
     "reg1": ["Register 1 Fault", "", "mdi:information-outline"],
     "reg2": ["Register 2 Fault", "", "mdi:information-outline"],
     "reg3": ["Register 3 Fault", "", "mdi:information-outline"],
-    "retpct": ["Restore Requirement", "%", "mdi:battery-alert"],
+    "retpct": ["Restore Requirement", UNIT_PERCENTAGE, "mdi:battery-alert"],
     "selftest": ["Last Self Test", "", "mdi:calendar-clock"],
     "sense": ["Sensitivity", "", "mdi:information-outline"],
     "serialno": ["Serial Number", "", "mdi:information-outline"],
@@ -92,14 +93,14 @@ SPECIFIC_UNITS = {"ITEMP": TEMP_CELSIUS}
 INFERRED_UNITS = {
     " Minutes": TIME_MINUTES,
     " Seconds": TIME_SECONDS,
-    " Percent": "%",
+    " Percent": UNIT_PERCENTAGE,
     " Volts": "V",
     " Ampere": "A",
     " Volt-Ampere": "VA",
     " Watts": POWER_WATT,
     " Hz": "Hz",
     " C": TEMP_CELSIUS,
-    " Percent Load Capacity": "%",
+    " Percent Load Capacity": UNIT_PERCENTAGE,
 }
 
 PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend(
diff --git a/homeassistant/components/aqualogic/sensor.py b/homeassistant/components/aqualogic/sensor.py
index 7fff009baa5..dde092dd1fa 100644
--- a/homeassistant/components/aqualogic/sensor.py
+++ b/homeassistant/components/aqualogic/sensor.py
@@ -4,7 +4,12 @@ import logging
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_MONITORED_CONDITIONS, TEMP_CELSIUS, TEMP_FAHRENHEIT
+from homeassistant.const import (
+    CONF_MONITORED_CONDITIONS,
+    TEMP_CELSIUS,
+    TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
+)
 from homeassistant.core import callback
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -14,7 +19,7 @@ from . import DOMAIN, UPDATE_TOPIC
 _LOGGER = logging.getLogger(__name__)
 
 TEMP_UNITS = [TEMP_CELSIUS, TEMP_FAHRENHEIT]
-PERCENT_UNITS = ["%", "%"]
+PERCENT_UNITS = [UNIT_PERCENTAGE, UNIT_PERCENTAGE]
 SALT_UNITS = ["g/L", "PPM"]
 WATT_UNITS = ["W", "W"]
 NO_UNITS = [None, None]
diff --git a/homeassistant/components/arlo/sensor.py b/homeassistant/components/arlo/sensor.py
index 5d11e9bc891..03e4437b257 100644
--- a/homeassistant/components/arlo/sensor.py
+++ b/homeassistant/components/arlo/sensor.py
@@ -11,6 +11,7 @@ from homeassistant.const import (
     DEVICE_CLASS_HUMIDITY,
     DEVICE_CLASS_TEMPERATURE,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import callback
 import homeassistant.helpers.config_validation as cv
@@ -27,10 +28,10 @@ SENSOR_TYPES = {
     "last_capture": ["Last", None, "run-fast"],
     "total_cameras": ["Arlo Cameras", None, "video"],
     "captured_today": ["Captured Today", None, "file-video"],
-    "battery_level": ["Battery Level", "%", "battery-50"],
+    "battery_level": ["Battery Level", UNIT_PERCENTAGE, "battery-50"],
     "signal_strength": ["Signal Strength", None, "signal"],
     "temperature": ["Temperature", TEMP_CELSIUS, "thermometer"],
-    "humidity": ["Humidity", "%", "water-percent"],
+    "humidity": ["Humidity", UNIT_PERCENTAGE, "water-percent"],
     "air_quality": ["Air Quality", CONCENTRATION_PARTS_PER_MILLION, "biohazard"],
 }
 
diff --git a/homeassistant/components/awair/sensor.py b/homeassistant/components/awair/sensor.py
index 18fb3f2cd54..301055c7e61 100644
--- a/homeassistant/components/awair/sensor.py
+++ b/homeassistant/components/awair/sensor.py
@@ -16,6 +16,7 @@ from homeassistant.const import (
     DEVICE_CLASS_HUMIDITY,
     DEVICE_CLASS_TEMPERATURE,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.exceptions import PlatformNotReady
 from homeassistant.helpers.aiohttp_client import async_get_clientsession
@@ -48,7 +49,7 @@ SENSOR_TYPES = {
     },
     "HUMID": {
         "device_class": DEVICE_CLASS_HUMIDITY,
-        "unit_of_measurement": "%",
+        "unit_of_measurement": UNIT_PERCENTAGE,
         "icon": "mdi:water-percent",
     },
     "CO2": {
@@ -80,7 +81,7 @@ SENSOR_TYPES = {
     },
     "score": {
         "device_class": DEVICE_CLASS_SCORE,
-        "unit_of_measurement": "%",
+        "unit_of_measurement": UNIT_PERCENTAGE,
         "icon": "mdi:percent",
     },
 }
diff --git a/homeassistant/components/beewi_smartclim/sensor.py b/homeassistant/components/beewi_smartclim/sensor.py
index 187ca411988..ec124b24971 100644
--- a/homeassistant/components/beewi_smartclim/sensor.py
+++ b/homeassistant/components/beewi_smartclim/sensor.py
@@ -12,6 +12,7 @@ from homeassistant.const import (
     DEVICE_CLASS_HUMIDITY,
     DEVICE_CLASS_TEMPERATURE,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -24,8 +25,8 @@ DEFAULT_NAME = "BeeWi SmartClim"
 # Sensor config
 SENSOR_TYPES = [
     [DEVICE_CLASS_TEMPERATURE, "Temperature", TEMP_CELSIUS],
-    [DEVICE_CLASS_HUMIDITY, "Humidity", "%"],
-    [DEVICE_CLASS_BATTERY, "Battery", "%"],
+    [DEVICE_CLASS_HUMIDITY, "Humidity", UNIT_PERCENTAGE],
+    [DEVICE_CLASS_BATTERY, "Battery", UNIT_PERCENTAGE],
 ]
 
 PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend(
diff --git a/homeassistant/components/bloomsky/sensor.py b/homeassistant/components/bloomsky/sensor.py
index 2ffdb8efab0..b07bca948bd 100644
--- a/homeassistant/components/bloomsky/sensor.py
+++ b/homeassistant/components/bloomsky/sensor.py
@@ -4,7 +4,12 @@ import logging
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_MONITORED_CONDITIONS, TEMP_CELSIUS, TEMP_FAHRENHEIT
+from homeassistant.const import (
+    CONF_MONITORED_CONDITIONS,
+    TEMP_CELSIUS,
+    TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
+)
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 
@@ -25,7 +30,7 @@ SENSOR_TYPES = [
 # Sensor units - these do not currently align with the API documentation
 SENSOR_UNITS_IMPERIAL = {
     "Temperature": TEMP_FAHRENHEIT,
-    "Humidity": "%",
+    "Humidity": UNIT_PERCENTAGE,
     "Pressure": "inHg",
     "Luminance": "cd/m²",
     "Voltage": "mV",
@@ -34,7 +39,7 @@ SENSOR_UNITS_IMPERIAL = {
 # Metric units
 SENSOR_UNITS_METRIC = {
     "Temperature": TEMP_CELSIUS,
-    "Humidity": "%",
+    "Humidity": UNIT_PERCENTAGE,
     "Pressure": "mbar",
     "Luminance": "cd/m²",
     "Voltage": "mV",
diff --git a/homeassistant/components/bme280/sensor.py b/homeassistant/components/bme280/sensor.py
index e1e33210c9b..28e22c10f20 100644
--- a/homeassistant/components/bme280/sensor.py
+++ b/homeassistant/components/bme280/sensor.py
@@ -8,7 +8,12 @@ import smbus  # pylint: disable=import-error
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_MONITORED_CONDITIONS, CONF_NAME, TEMP_FAHRENHEIT
+from homeassistant.const import (
+    CONF_MONITORED_CONDITIONS,
+    CONF_NAME,
+    TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
+)
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 from homeassistant.util import Throttle
@@ -44,7 +49,7 @@ SENSOR_HUMID = "humidity"
 SENSOR_PRESS = "pressure"
 SENSOR_TYPES = {
     SENSOR_TEMP: ["Temperature", None],
-    SENSOR_HUMID: ["Humidity", "%"],
+    SENSOR_HUMID: ["Humidity", UNIT_PERCENTAGE],
     SENSOR_PRESS: ["Pressure", "mb"],
 }
 DEFAULT_MONITORED = [SENSOR_TEMP, SENSOR_HUMID, SENSOR_PRESS]
diff --git a/homeassistant/components/bme680/sensor.py b/homeassistant/components/bme680/sensor.py
index 43430f724bb..19d6fbd3086 100644
--- a/homeassistant/components/bme680/sensor.py
+++ b/homeassistant/components/bme680/sensor.py
@@ -8,7 +8,12 @@ from smbus import SMBus  # pylint: disable=import-error
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_MONITORED_CONDITIONS, CONF_NAME, TEMP_FAHRENHEIT
+from homeassistant.const import (
+    CONF_MONITORED_CONDITIONS,
+    CONF_NAME,
+    TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
+)
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 from homeassistant.util.temperature import celsius_to_fahrenheit
@@ -50,10 +55,10 @@ SENSOR_GAS = "gas"
 SENSOR_AQ = "airquality"
 SENSOR_TYPES = {
     SENSOR_TEMP: ["Temperature", None],
-    SENSOR_HUMID: ["Humidity", "%"],
+    SENSOR_HUMID: ["Humidity", UNIT_PERCENTAGE],
     SENSOR_PRESS: ["Pressure", "mb"],
     SENSOR_GAS: ["Gas Resistance", "Ohms"],
-    SENSOR_AQ: ["Air Quality", "%"],
+    SENSOR_AQ: ["Air Quality", UNIT_PERCENTAGE],
 }
 DEFAULT_MONITORED = [SENSOR_TEMP, SENSOR_HUMID, SENSOR_PRESS, SENSOR_AQ]
 OVERSAMPLING_VALUES = set([0, 1, 2, 4, 8, 16])
diff --git a/homeassistant/components/bmw_connected_drive/sensor.py b/homeassistant/components/bmw_connected_drive/sensor.py
index 7fb3da8b883..30c12d7d7a0 100644
--- a/homeassistant/components/bmw_connected_drive/sensor.py
+++ b/homeassistant/components/bmw_connected_drive/sensor.py
@@ -8,6 +8,7 @@ from homeassistant.const import (
     LENGTH_KILOMETERS,
     LENGTH_MILES,
     TIME_HOURS,
+    UNIT_PERCENTAGE,
     VOLUME_GALLONS,
     VOLUME_LITERS,
 )
@@ -28,7 +29,7 @@ ATTR_TO_HA_METRIC = {
     "charging_time_remaining": ["mdi:update", TIME_HOURS],
     "charging_status": ["mdi:battery-charging", None],
     # No icon as this is dealt with directly as a special case in icon()
-    "charging_level_hv": [None, "%"],
+    "charging_level_hv": [None, UNIT_PERCENTAGE],
 }
 
 ATTR_TO_HA_IMPERIAL = {
@@ -41,7 +42,7 @@ ATTR_TO_HA_IMPERIAL = {
     "charging_time_remaining": ["mdi:update", TIME_HOURS],
     "charging_status": ["mdi:battery-charging", None],
     # No icon as this is dealt with directly as a special case in icon()
-    "charging_level_hv": [None, "%"],
+    "charging_level_hv": [None, UNIT_PERCENTAGE],
 }
 
 
diff --git a/homeassistant/components/bom/sensor.py b/homeassistant/components/bom/sensor.py
index 836a2a79509..5ecd9c1009f 100644
--- a/homeassistant/components/bom/sensor.py
+++ b/homeassistant/components/bom/sensor.py
@@ -21,6 +21,7 @@ from homeassistant.const import (
     CONF_NAME,
     SPEED_KILOMETERS_PER_HOUR,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -68,7 +69,7 @@ SENSOR_TYPES = {
     "press_msl": ["Pressure msl", "msl"],
     "press_tend": ["Pressure Tend", None],
     "rain_trace": ["Rain Today", "mm"],
-    "rel_hum": ["Relative Humidity", "%"],
+    "rel_hum": ["Relative Humidity", UNIT_PERCENTAGE],
     "sea_state": ["Sea State", None],
     "swell_dir_worded": ["Swell Direction", None],
     "swell_height": ["Swell Height", "m"],
diff --git a/homeassistant/components/broadlink/sensor.py b/homeassistant/components/broadlink/sensor.py
index 408593e337d..dbff4108a3f 100644
--- a/homeassistant/components/broadlink/sensor.py
+++ b/homeassistant/components/broadlink/sensor.py
@@ -15,6 +15,7 @@ from homeassistant.const import (
     CONF_SCAN_INTERVAL,
     CONF_TIMEOUT,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -29,7 +30,7 @@ SCAN_INTERVAL = timedelta(seconds=300)
 SENSOR_TYPES = {
     "temperature": ["Temperature", TEMP_CELSIUS],
     "air_quality": ["Air Quality", " "],
-    "humidity": ["Humidity", "%"],
+    "humidity": ["Humidity", UNIT_PERCENTAGE],
     "light": ["Light", " "],
     "noise": ["Noise", " "],
 }
diff --git a/homeassistant/components/brother/const.py b/homeassistant/components/brother/const.py
index d3b7c5e2a78..e887ad6de21 100644
--- a/homeassistant/components/brother/const.py
+++ b/homeassistant/components/brother/const.py
@@ -1,5 +1,5 @@
 """Constants for Brother integration."""
-from homeassistant.const import TIME_DAYS
+from homeassistant.const import TIME_DAYS, UNIT_PERCENTAGE
 
 ATTR_BELT_UNIT_REMAINING_LIFE = "belt_unit_remaining_life"
 ATTR_BLACK_INK_REMAINING = "black_ink_remaining"
@@ -30,7 +30,6 @@ ATTR_YELLOW_TONER_REMAINING = "yellow_toner_remaining"
 DOMAIN = "brother"
 
 UNIT_PAGES = "p"
-UNIT_PERCENT = "%"
 
 PRINTER_TYPES = ["laser", "ink"]
 
@@ -58,72 +57,72 @@ SENSOR_TYPES = {
     ATTR_DRUM_REMAINING_LIFE: {
         ATTR_ICON: "mdi:chart-donut",
         ATTR_LABEL: ATTR_DRUM_REMAINING_LIFE.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_BELT_UNIT_REMAINING_LIFE: {
         ATTR_ICON: "mdi:current-ac",
         ATTR_LABEL: ATTR_BELT_UNIT_REMAINING_LIFE.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_FUSER_REMAINING_LIFE: {
         ATTR_ICON: "mdi:water-outline",
         ATTR_LABEL: ATTR_FUSER_REMAINING_LIFE.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_LASER_REMAINING_LIFE: {
         ATTR_ICON: "mdi:spotlight-beam",
         ATTR_LABEL: ATTR_LASER_REMAINING_LIFE.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_PF_KIT_1_REMAINING_LIFE: {
         ATTR_ICON: "mdi:printer-3d",
         ATTR_LABEL: ATTR_PF_KIT_1_REMAINING_LIFE.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_PF_KIT_MP_REMAINING_LIFE: {
         ATTR_ICON: "mdi:printer-3d",
         ATTR_LABEL: ATTR_PF_KIT_MP_REMAINING_LIFE.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_BLACK_TONER_REMAINING: {
         ATTR_ICON: "mdi:printer-3d-nozzle",
         ATTR_LABEL: ATTR_BLACK_TONER_REMAINING.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_CYAN_TONER_REMAINING: {
         ATTR_ICON: "mdi:printer-3d-nozzle",
         ATTR_LABEL: ATTR_CYAN_TONER_REMAINING.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_MAGENTA_TONER_REMAINING: {
         ATTR_ICON: "mdi:printer-3d-nozzle",
         ATTR_LABEL: ATTR_MAGENTA_TONER_REMAINING.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_YELLOW_TONER_REMAINING: {
         ATTR_ICON: "mdi:printer-3d-nozzle",
         ATTR_LABEL: ATTR_YELLOW_TONER_REMAINING.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_BLACK_INK_REMAINING: {
         ATTR_ICON: "mdi:printer-3d-nozzle",
         ATTR_LABEL: ATTR_BLACK_INK_REMAINING.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_CYAN_INK_REMAINING: {
         ATTR_ICON: "mdi:printer-3d-nozzle",
         ATTR_LABEL: ATTR_CYAN_INK_REMAINING.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_MAGENTA_INK_REMAINING: {
         ATTR_ICON: "mdi:printer-3d-nozzle",
         ATTR_LABEL: ATTR_MAGENTA_INK_REMAINING.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_YELLOW_INK_REMAINING: {
         ATTR_ICON: "mdi:printer-3d-nozzle",
         ATTR_LABEL: ATTR_YELLOW_INK_REMAINING.replace("_", " ").title(),
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
     },
     ATTR_UPTIME: {
         ATTR_ICON: "mdi:timer",
diff --git a/homeassistant/components/buienradar/sensor.py b/homeassistant/components/buienradar/sensor.py
index 32ecf50ed9d..5d709ab1e63 100644
--- a/homeassistant/components/buienradar/sensor.py
+++ b/homeassistant/components/buienradar/sensor.py
@@ -31,6 +31,7 @@ from homeassistant.const import (
     SPEED_KILOMETERS_PER_HOUR,
     TEMP_CELSIUS,
     TIME_HOURS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -67,7 +68,7 @@ SENSOR_TYPES = {
     "symbol": ["Symbol", None, None],
     # new in json api (>1.0.0):
     "feeltemperature": ["Feel temperature", TEMP_CELSIUS, "mdi:thermometer"],
-    "humidity": ["Humidity", "%", "mdi:water-percent"],
+    "humidity": ["Humidity", UNIT_PERCENTAGE, "mdi:water-percent"],
     "temperature": ["Temperature", TEMP_CELSIUS, "mdi:thermometer"],
     "groundtemperature": ["Ground temperature", TEMP_CELSIUS, "mdi:thermometer"],
     "windspeed": ["Wind speed", SPEED_KILOMETERS_PER_HOUR, "mdi:weather-windy"],
@@ -120,16 +121,16 @@ SENSOR_TYPES = {
     "maxrain_3d": ["Maximum rain 3d", "mm", "mdi:weather-pouring"],
     "maxrain_4d": ["Maximum rain 4d", "mm", "mdi:weather-pouring"],
     "maxrain_5d": ["Maximum rain 5d", "mm", "mdi:weather-pouring"],
-    "rainchance_1d": ["Rainchance 1d", "%", "mdi:weather-pouring"],
-    "rainchance_2d": ["Rainchance 2d", "%", "mdi:weather-pouring"],
-    "rainchance_3d": ["Rainchance 3d", "%", "mdi:weather-pouring"],
-    "rainchance_4d": ["Rainchance 4d", "%", "mdi:weather-pouring"],
-    "rainchance_5d": ["Rainchance 5d", "%", "mdi:weather-pouring"],
-    "sunchance_1d": ["Sunchance 1d", "%", "mdi:weather-partly-cloudy"],
-    "sunchance_2d": ["Sunchance 2d", "%", "mdi:weather-partly-cloudy"],
-    "sunchance_3d": ["Sunchance 3d", "%", "mdi:weather-partly-cloudy"],
-    "sunchance_4d": ["Sunchance 4d", "%", "mdi:weather-partly-cloudy"],
-    "sunchance_5d": ["Sunchance 5d", "%", "mdi:weather-partly-cloudy"],
+    "rainchance_1d": ["Rainchance 1d", UNIT_PERCENTAGE, "mdi:weather-pouring"],
+    "rainchance_2d": ["Rainchance 2d", UNIT_PERCENTAGE, "mdi:weather-pouring"],
+    "rainchance_3d": ["Rainchance 3d", UNIT_PERCENTAGE, "mdi:weather-pouring"],
+    "rainchance_4d": ["Rainchance 4d", UNIT_PERCENTAGE, "mdi:weather-pouring"],
+    "rainchance_5d": ["Rainchance 5d", UNIT_PERCENTAGE, "mdi:weather-pouring"],
+    "sunchance_1d": ["Sunchance 1d", UNIT_PERCENTAGE, "mdi:weather-partly-cloudy"],
+    "sunchance_2d": ["Sunchance 2d", UNIT_PERCENTAGE, "mdi:weather-partly-cloudy"],
+    "sunchance_3d": ["Sunchance 3d", UNIT_PERCENTAGE, "mdi:weather-partly-cloudy"],
+    "sunchance_4d": ["Sunchance 4d", UNIT_PERCENTAGE, "mdi:weather-partly-cloudy"],
+    "sunchance_5d": ["Sunchance 5d", UNIT_PERCENTAGE, "mdi:weather-partly-cloudy"],
     "windforce_1d": ["Wind force 1d", "Bft", "mdi:weather-windy"],
     "windforce_2d": ["Wind force 2d", "Bft", "mdi:weather-windy"],
     "windforce_3d": ["Wind force 3d", "Bft", "mdi:weather-windy"],
diff --git a/homeassistant/components/canary/sensor.py b/homeassistant/components/canary/sensor.py
index 67654c99f3e..09413f9cb61 100644
--- a/homeassistant/components/canary/sensor.py
+++ b/homeassistant/components/canary/sensor.py
@@ -1,7 +1,7 @@
 """Support for Canary sensors."""
 from canary.api import SensorType
 
-from homeassistant.const import TEMP_CELSIUS
+from homeassistant.const import TEMP_CELSIUS, UNIT_PERCENTAGE
 from homeassistant.helpers.entity import Entity
 from homeassistant.helpers.icon import icon_for_battery_level
 
@@ -14,10 +14,10 @@ ATTR_AIR_QUALITY = "air_quality"
 # sensor type name, unit_of_measurement, icon
 SENSOR_TYPES = [
     ["temperature", TEMP_CELSIUS, "mdi:thermometer", ["Canary"]],
-    ["humidity", "%", "mdi:water-percent", ["Canary"]],
+    ["humidity", UNIT_PERCENTAGE, "mdi:water-percent", ["Canary"]],
     ["air_quality", None, "mdi:weather-windy", ["Canary"]],
     ["wifi", "dBm", "mdi:wifi", ["Canary Flex"]],
-    ["battery", "%", "mdi:battery-50", ["Canary Flex"]],
+    ["battery", UNIT_PERCENTAGE, "mdi:battery-50", ["Canary Flex"]],
 ]
 
 STATE_AIR_QUALITY_NORMAL = "normal"
diff --git a/homeassistant/components/climate/device_trigger.py b/homeassistant/components/climate/device_trigger.py
index 4c5dcb0ee04..187f50bc984 100644
--- a/homeassistant/components/climate/device_trigger.py
+++ b/homeassistant/components/climate/device_trigger.py
@@ -18,6 +18,7 @@ from homeassistant.const import (
     CONF_FOR,
     CONF_PLATFORM,
     CONF_TYPE,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import CALLBACK_TYPE, HomeAssistant
 from homeassistant.helpers import config_validation as cv, entity_registry
@@ -177,7 +178,7 @@ async def async_get_trigger_capabilities(hass: HomeAssistant, config):
     if trigger_type == "current_temperature_changed":
         unit_of_measurement = hass.config.units.temperature_unit
     else:
-        unit_of_measurement = "%"
+        unit_of_measurement = UNIT_PERCENTAGE
 
     return {
         "extra_fields": vol.Schema(
diff --git a/homeassistant/components/comfoconnect/sensor.py b/homeassistant/components/comfoconnect/sensor.py
index 1d189508960..5c8c0d6a75c 100644
--- a/homeassistant/components/comfoconnect/sensor.py
+++ b/homeassistant/components/comfoconnect/sensor.py
@@ -33,6 +33,7 @@ from homeassistant.const import (
     TEMP_CELSIUS,
     TIME_DAYS,
     TIME_HOURS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.dispatcher import async_dispatcher_connect
@@ -78,7 +79,7 @@ SENSOR_TYPES = {
     ATTR_CURRENT_HUMIDITY: {
         ATTR_DEVICE_CLASS: DEVICE_CLASS_HUMIDITY,
         ATTR_LABEL: "Inside Humidity",
-        ATTR_UNIT: "%",
+        ATTR_UNIT: UNIT_PERCENTAGE,
         ATTR_ICON: "mdi:water-percent",
         ATTR_ID: SENSOR_HUMIDITY_EXTRACT,
     },
@@ -93,7 +94,7 @@ SENSOR_TYPES = {
     ATTR_OUTSIDE_HUMIDITY: {
         ATTR_DEVICE_CLASS: DEVICE_CLASS_HUMIDITY,
         ATTR_LABEL: "Outside Humidity",
-        ATTR_UNIT: "%",
+        ATTR_UNIT: UNIT_PERCENTAGE,
         ATTR_ICON: "mdi:water-percent",
         ATTR_ID: SENSOR_HUMIDITY_OUTDOOR,
     },
@@ -108,7 +109,7 @@ SENSOR_TYPES = {
     ATTR_SUPPLY_HUMIDITY: {
         ATTR_DEVICE_CLASS: DEVICE_CLASS_HUMIDITY,
         ATTR_LABEL: "Supply Humidity",
-        ATTR_UNIT: "%",
+        ATTR_UNIT: UNIT_PERCENTAGE,
         ATTR_ICON: "mdi:water-percent",
         ATTR_ID: SENSOR_HUMIDITY_SUPPLY,
     },
@@ -122,7 +123,7 @@ SENSOR_TYPES = {
     ATTR_SUPPLY_FAN_DUTY: {
         ATTR_DEVICE_CLASS: None,
         ATTR_LABEL: "Supply Fan Duty",
-        ATTR_UNIT: "%",
+        ATTR_UNIT: UNIT_PERCENTAGE,
         ATTR_ICON: "mdi:fan",
         ATTR_ID: SENSOR_FAN_SUPPLY_DUTY,
     },
@@ -136,7 +137,7 @@ SENSOR_TYPES = {
     ATTR_EXHAUST_FAN_DUTY: {
         ATTR_DEVICE_CLASS: None,
         ATTR_LABEL: "Exhaust Fan Duty",
-        ATTR_UNIT: "%",
+        ATTR_UNIT: UNIT_PERCENTAGE,
         ATTR_ICON: "mdi:fan",
         ATTR_ID: SENSOR_FAN_EXHAUST_DUTY,
     },
@@ -151,7 +152,7 @@ SENSOR_TYPES = {
     ATTR_EXHAUST_HUMIDITY: {
         ATTR_DEVICE_CLASS: DEVICE_CLASS_HUMIDITY,
         ATTR_LABEL: "Exhaust Humidity",
-        ATTR_UNIT: "%",
+        ATTR_UNIT: UNIT_PERCENTAGE,
         ATTR_ICON: "mdi:water-percent",
         ATTR_ID: SENSOR_HUMIDITY_EXHAUST,
     },
@@ -172,7 +173,7 @@ SENSOR_TYPES = {
     ATTR_BYPASS_STATE: {
         ATTR_DEVICE_CLASS: None,
         ATTR_LABEL: "Bypass State",
-        ATTR_UNIT: "%",
+        ATTR_UNIT: UNIT_PERCENTAGE,
         ATTR_ICON: "mdi:camera-iris",
         ATTR_ID: SENSOR_BYPASS_STATE,
     },
diff --git a/homeassistant/components/cups/sensor.py b/homeassistant/components/cups/sensor.py
index 7581891af6a..ac158388242 100644
--- a/homeassistant/components/cups/sensor.py
+++ b/homeassistant/components/cups/sensor.py
@@ -6,7 +6,7 @@ import logging
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_HOST, CONF_PORT
+from homeassistant.const import CONF_HOST, CONF_PORT, UNIT_PERCENTAGE
 from homeassistant.exceptions import PlatformNotReady
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -268,7 +268,7 @@ class MarkerSensor(Entity):
     @property
     def unit_of_measurement(self):
         """Return the unit of measurement."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     @property
     def device_state_attributes(self):
diff --git a/homeassistant/components/danfoss_air/sensor.py b/homeassistant/components/danfoss_air/sensor.py
index 247eb955154..73305d5c625 100644
--- a/homeassistant/components/danfoss_air/sensor.py
+++ b/homeassistant/components/danfoss_air/sensor.py
@@ -6,6 +6,7 @@ from homeassistant.const import (
     DEVICE_CLASS_HUMIDITY,
     DEVICE_CLASS_TEMPERATURE,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.entity import Entity
 
@@ -45,14 +46,24 @@ def setup_platform(hass, config, add_entities, discovery_info=None):
             ReadCommand.extractTemperature,
             DEVICE_CLASS_TEMPERATURE,
         ],
-        ["Danfoss Air Remaining Filter", "%", ReadCommand.filterPercent, None],
-        ["Danfoss Air Humidity", "%", ReadCommand.humidity, DEVICE_CLASS_HUMIDITY],
-        ["Danfoss Air Fan Step", "%", ReadCommand.fan_step, None],
+        [
+            "Danfoss Air Remaining Filter",
+            UNIT_PERCENTAGE,
+            ReadCommand.filterPercent,
+            None,
+        ],
+        [
+            "Danfoss Air Humidity",
+            UNIT_PERCENTAGE,
+            ReadCommand.humidity,
+            DEVICE_CLASS_HUMIDITY,
+        ],
+        ["Danfoss Air Fan Step", UNIT_PERCENTAGE, ReadCommand.fan_step, None],
         ["Danfoss Air Exhaust Fan Speed", "RPM", ReadCommand.exhaust_fan_speed, None],
         ["Danfoss Air Supply Fan Speed", "RPM", ReadCommand.supply_fan_speed, None],
         [
             "Danfoss Air Dial Battery",
-            "%",
+            UNIT_PERCENTAGE,
             ReadCommand.battery_percent,
             DEVICE_CLASS_BATTERY,
         ],
diff --git a/homeassistant/components/darksky/sensor.py b/homeassistant/components/darksky/sensor.py
index 46741e3aca7..26ba590888f 100644
--- a/homeassistant/components/darksky/sensor.py
+++ b/homeassistant/components/darksky/sensor.py
@@ -19,6 +19,7 @@ from homeassistant.const import (
     SPEED_METERS_PER_SECOND,
     SPEED_MILES_PER_HOUR,
     TIME_HOURS,
+    UNIT_PERCENTAGE,
     UNIT_UV_INDEX,
 )
 import homeassistant.helpers.config_validation as cv
@@ -113,11 +114,11 @@ SENSOR_TYPES = {
     ],
     "precip_probability": [
         "Precip Probability",
-        "%",
-        "%",
-        "%",
-        "%",
-        "%",
+        UNIT_PERCENTAGE,
+        UNIT_PERCENTAGE,
+        UNIT_PERCENTAGE,
+        UNIT_PERCENTAGE,
+        UNIT_PERCENTAGE,
         "mdi:water-percent",
         ["currently", "minutely", "hourly", "daily"],
     ],
@@ -193,21 +194,21 @@ SENSOR_TYPES = {
     ],
     "cloud_cover": [
         "Cloud Coverage",
-        "%",
-        "%",
-        "%",
-        "%",
-        "%",
+        UNIT_PERCENTAGE,
+        UNIT_PERCENTAGE,
+        UNIT_PERCENTAGE,
+        UNIT_PERCENTAGE,
+        UNIT_PERCENTAGE,
         "mdi:weather-partly-cloudy",
         ["currently", "hourly", "daily"],
     ],
     "humidity": [
         "Humidity",
-        "%",
-        "%",
-        "%",
-        "%",
-        "%",
+        UNIT_PERCENTAGE,
+        UNIT_PERCENTAGE,
+        UNIT_PERCENTAGE,
+        UNIT_PERCENTAGE,
+        UNIT_PERCENTAGE,
         "mdi:water-percent",
         ["currently", "hourly", "daily"],
     ],
diff --git a/homeassistant/components/deconz/sensor.py b/homeassistant/components/deconz/sensor.py
index c32b26f299d..fd8ffeeaaf0 100644
--- a/homeassistant/components/deconz/sensor.py
+++ b/homeassistant/components/deconz/sensor.py
@@ -9,7 +9,12 @@ from pydeconz.sensor import (
     Thermostat,
 )
 
-from homeassistant.const import ATTR_TEMPERATURE, ATTR_VOLTAGE, DEVICE_CLASS_BATTERY
+from homeassistant.const import (
+    ATTR_TEMPERATURE,
+    ATTR_VOLTAGE,
+    DEVICE_CLASS_BATTERY,
+    UNIT_PERCENTAGE,
+)
 from homeassistant.core import callback
 from homeassistant.helpers.dispatcher import (
     async_dispatcher_connect,
@@ -194,7 +199,7 @@ class DeconzBattery(DeconzDevice):
     @property
     def unit_of_measurement(self):
         """Return the unit of measurement of this entity."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     @property
     def device_state_attributes(self):
diff --git a/homeassistant/components/demo/sensor.py b/homeassistant/components/demo/sensor.py
index d2b2464468b..6805ebb5b56 100644
--- a/homeassistant/components/demo/sensor.py
+++ b/homeassistant/components/demo/sensor.py
@@ -4,6 +4,7 @@ from homeassistant.const import (
     DEVICE_CLASS_HUMIDITY,
     DEVICE_CLASS_TEMPERATURE,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.entity import Entity
 
@@ -23,7 +24,12 @@ async def async_setup_platform(hass, config, async_add_entities, discovery_info=
                 12,
             ),
             DemoSensor(
-                "sensor_2", "Outside Humidity", 54, DEVICE_CLASS_HUMIDITY, "%", None
+                "sensor_2",
+                "Outside Humidity",
+                54,
+                DEVICE_CLASS_HUMIDITY,
+                UNIT_PERCENTAGE,
+                None,
             ),
         ]
     )
diff --git a/homeassistant/components/dht/sensor.py b/homeassistant/components/dht/sensor.py
index 26b0493cb99..b9461fae7d7 100644
--- a/homeassistant/components/dht/sensor.py
+++ b/homeassistant/components/dht/sensor.py
@@ -6,7 +6,12 @@ import Adafruit_DHT  # pylint: disable=import-error
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_MONITORED_CONDITIONS, CONF_NAME, TEMP_FAHRENHEIT
+from homeassistant.const import (
+    CONF_MONITORED_CONDITIONS,
+    CONF_NAME,
+    TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
+)
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 from homeassistant.util import Throttle
@@ -28,7 +33,7 @@ SENSOR_TEMPERATURE = "temperature"
 SENSOR_HUMIDITY = "humidity"
 SENSOR_TYPES = {
     SENSOR_TEMPERATURE: ["Temperature", None],
-    SENSOR_HUMIDITY: ["Humidity", "%"],
+    SENSOR_HUMIDITY: ["Humidity", UNIT_PERCENTAGE],
 }
 
 PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend(
diff --git a/homeassistant/components/dovado/sensor.py b/homeassistant/components/dovado/sensor.py
index 5e3745b27ed..8328df8bd7f 100644
--- a/homeassistant/components/dovado/sensor.py
+++ b/homeassistant/components/dovado/sensor.py
@@ -6,7 +6,7 @@ import re
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_SENSORS, DATA_GIGABYTES
+from homeassistant.const import CONF_SENSORS, DATA_GIGABYTES, UNIT_PERCENTAGE
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 
@@ -24,7 +24,12 @@ SENSOR_SMS_UNREAD = "sms"
 
 SENSORS = {
     SENSOR_NETWORK: ("signal strength", "Network", None, "mdi:access-point-network"),
-    SENSOR_SIGNAL: ("signal strength", "Signal Strength", "%", "mdi:signal"),
+    SENSOR_SIGNAL: (
+        "signal strength",
+        "Signal Strength",
+        UNIT_PERCENTAGE,
+        "mdi:signal",
+    ),
     SENSOR_SMS_UNREAD: ("sms unread", "SMS unread", "", "mdi:message-text-outline"),
     SENSOR_UPLOAD: ("traffic modem tx", "Sent", DATA_GIGABYTES, "mdi:cloud-upload"),
     SENSOR_DOWNLOAD: (
diff --git a/homeassistant/components/dyson/sensor.py b/homeassistant/components/dyson/sensor.py
index c7f61422a2e..55f2ff69314 100644
--- a/homeassistant/components/dyson/sensor.py
+++ b/homeassistant/components/dyson/sensor.py
@@ -4,7 +4,7 @@ import logging
 from libpurecool.dyson_pure_cool import DysonPureCool
 from libpurecool.dyson_pure_cool_link import DysonPureCoolLink
 
-from homeassistant.const import STATE_OFF, TEMP_CELSIUS, TIME_HOURS
+from homeassistant.const import STATE_OFF, TEMP_CELSIUS, TIME_HOURS, UNIT_PERCENTAGE
 from homeassistant.helpers.entity import Entity
 
 from . import DYSON_DEVICES
@@ -13,7 +13,7 @@ SENSOR_UNITS = {
     "air_quality": None,
     "dust": None,
     "filter_life": TIME_HOURS,
-    "humidity": "%",
+    "humidity": UNIT_PERCENTAGE,
 }
 
 SENSOR_ICONS = {
diff --git a/homeassistant/components/ebox/sensor.py b/homeassistant/components/ebox/sensor.py
index 208ffb99543..dc150109cf7 100644
--- a/homeassistant/components/ebox/sensor.py
+++ b/homeassistant/components/ebox/sensor.py
@@ -18,6 +18,7 @@ from homeassistant.const import (
     CONF_USERNAME,
     DATA_GIGABITS,
     TIME_DAYS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.exceptions import PlatformNotReady
 import homeassistant.helpers.config_validation as cv
@@ -27,7 +28,6 @@ from homeassistant.util import Throttle
 _LOGGER = logging.getLogger(__name__)
 
 PRICE = "CAD"
-PERCENT = "%"
 
 DEFAULT_NAME = "EBox"
 
@@ -36,7 +36,7 @@ SCAN_INTERVAL = timedelta(minutes=15)
 MIN_TIME_BETWEEN_UPDATES = timedelta(minutes=15)
 
 SENSOR_TYPES = {
-    "usage": ["Usage", PERCENT, "mdi:percent"],
+    "usage": ["Usage", UNIT_PERCENTAGE, "mdi:percent"],
     "balance": ["Balance", PRICE, "mdi:square-inc-cash"],
     "limit": ["Data limit", DATA_GIGABITS, "mdi:download"],
     "days_left": ["Days left", TIME_DAYS, "mdi:calendar-today"],
diff --git a/homeassistant/components/ecobee/sensor.py b/homeassistant/components/ecobee/sensor.py
index ca3e7732e1b..e510cc976a6 100644
--- a/homeassistant/components/ecobee/sensor.py
+++ b/homeassistant/components/ecobee/sensor.py
@@ -5,6 +5,7 @@ from homeassistant.const import (
     DEVICE_CLASS_HUMIDITY,
     DEVICE_CLASS_TEMPERATURE,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.entity import Entity
 
@@ -12,7 +13,7 @@ from .const import _LOGGER, DOMAIN, ECOBEE_MODEL_TO_NAME, MANUFACTURER
 
 SENSOR_TYPES = {
     "temperature": ["Temperature", TEMP_FAHRENHEIT],
-    "humidity": ["Humidity", "%"],
+    "humidity": ["Humidity", UNIT_PERCENTAGE],
 }
 
 
diff --git a/homeassistant/components/eight_sleep/sensor.py b/homeassistant/components/eight_sleep/sensor.py
index af6de2657ce..457323d3bd5 100644
--- a/homeassistant/components/eight_sleep/sensor.py
+++ b/homeassistant/components/eight_sleep/sensor.py
@@ -1,6 +1,8 @@
 """Support for Eight Sleep sensors."""
 import logging
 
+from homeassistant.const import UNIT_PERCENTAGE
+
 from . import (
     CONF_SENSORS,
     DATA_EIGHT,
@@ -18,9 +20,9 @@ ATTR_AVG_RESP_RATE = "Average Respiratory Rate"
 ATTR_HEART_RATE = "Heart Rate"
 ATTR_AVG_HEART_RATE = "Average Heart Rate"
 ATTR_SLEEP_DUR = "Time Slept"
-ATTR_LIGHT_PERC = "Light Sleep %"
-ATTR_DEEP_PERC = "Deep Sleep %"
-ATTR_REM_PERC = "REM Sleep %"
+ATTR_LIGHT_PERC = f"Light Sleep {UNIT_PERCENTAGE}"
+ATTR_DEEP_PERC = f"Deep Sleep {UNIT_PERCENTAGE}"
+ATTR_REM_PERC = f"REM Sleep {UNIT_PERCENTAGE}"
 ATTR_TNT = "Tosses & Turns"
 ATTR_SLEEP_STAGE = "Sleep Stage"
 ATTR_TARGET_HEAT = "Target Heating Level"
@@ -100,7 +102,7 @@ class EightHeatSensor(EightSleepHeatEntity):
     @property
     def unit_of_measurement(self):
         """Return the unit the value is expressed in."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     async def async_update(self):
         """Retrieve latest state."""
diff --git a/homeassistant/components/enocean/sensor.py b/homeassistant/components/enocean/sensor.py
index 5cf908a33a1..45a20197a4a 100644
--- a/homeassistant/components/enocean/sensor.py
+++ b/homeassistant/components/enocean/sensor.py
@@ -16,6 +16,7 @@ from homeassistant.const import (
     STATE_CLOSED,
     STATE_OPEN,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 
@@ -36,7 +37,7 @@ SENSOR_TYPE_WINDOWHANDLE = "windowhandle"
 SENSOR_TYPES = {
     SENSOR_TYPE_HUMIDITY: {
         "name": "Humidity",
-        "unit": "%",
+        "unit": UNIT_PERCENTAGE,
         "icon": "mdi:water-percent",
         "class": DEVICE_CLASS_HUMIDITY,
     },
diff --git a/homeassistant/components/epsonworkforce/sensor.py b/homeassistant/components/epsonworkforce/sensor.py
index 3bb90eb0644..b2164325547 100644
--- a/homeassistant/components/epsonworkforce/sensor.py
+++ b/homeassistant/components/epsonworkforce/sensor.py
@@ -6,19 +6,19 @@ from epsonprinter_pkg.epsonprinterapi import EpsonPrinterAPI
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_HOST, CONF_MONITORED_CONDITIONS
+from homeassistant.const import CONF_HOST, CONF_MONITORED_CONDITIONS, UNIT_PERCENTAGE
 from homeassistant.exceptions import PlatformNotReady
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 
 _LOGGER = logging.getLogger(__name__)
 MONITORED_CONDITIONS = {
-    "black": ["Ink level Black", "%", "mdi:water"],
-    "photoblack": ["Ink level Photoblack", "%", "mdi:water"],
-    "magenta": ["Ink level Magenta", "%", "mdi:water"],
-    "cyan": ["Ink level Cyan", "%", "mdi:water"],
-    "yellow": ["Ink level Yellow", "%", "mdi:water"],
-    "clean": ["Cleaning level", "%", "mdi:water"],
+    "black": ["Ink level Black", UNIT_PERCENTAGE, "mdi:water"],
+    "photoblack": ["Ink level Photoblack", UNIT_PERCENTAGE, "mdi:water"],
+    "magenta": ["Ink level Magenta", UNIT_PERCENTAGE, "mdi:water"],
+    "cyan": ["Ink level Cyan", UNIT_PERCENTAGE, "mdi:water"],
+    "yellow": ["Ink level Yellow", UNIT_PERCENTAGE, "mdi:water"],
+    "clean": ["Cleaning level", UNIT_PERCENTAGE, "mdi:water"],
 }
 PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend(
     {
diff --git a/homeassistant/components/fibaro/sensor.py b/homeassistant/components/fibaro/sensor.py
index 5fce0da7a2b..68a39431a98 100644
--- a/homeassistant/components/fibaro/sensor.py
+++ b/homeassistant/components/fibaro/sensor.py
@@ -9,6 +9,7 @@ from homeassistant.const import (
     DEVICE_CLASS_TEMPERATURE,
     TEMP_CELSIUS,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.entity import Entity
 
@@ -28,7 +29,12 @@ SENSOR_TYPES = {
         None,
     ],
     "CO2": ["CO2", CONCENTRATION_PARTS_PER_MILLION, "mdi:cloud", None],
-    "com.fibaro.humiditySensor": ["Humidity", "%", None, DEVICE_CLASS_HUMIDITY],
+    "com.fibaro.humiditySensor": [
+        "Humidity",
+        UNIT_PERCENTAGE,
+        None,
+        DEVICE_CLASS_HUMIDITY,
+    ],
     "com.fibaro.lightSensor": ["Light", "lx", None, DEVICE_CLASS_ILLUMINANCE],
 }
 
diff --git a/homeassistant/components/fitbit/sensor.py b/homeassistant/components/fitbit/sensor.py
index b6a4fe550c9..66c283f20ef 100644
--- a/homeassistant/components/fitbit/sensor.py
+++ b/homeassistant/components/fitbit/sensor.py
@@ -18,6 +18,7 @@ from homeassistant.const import (
     MASS_MILLIGRAMS,
     TIME_MILLISECONDS,
     TIME_MINUTES,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import callback
 import homeassistant.helpers.config_validation as cv
@@ -91,11 +92,11 @@ FITBIT_RESOURCES_LIST = {
     ],
     "activities/tracker/steps": ["Tracker Steps", "steps", "walk"],
     "body/bmi": ["BMI", "BMI", "human"],
-    "body/fat": ["Body Fat", "%", "human"],
+    "body/fat": ["Body Fat", UNIT_PERCENTAGE, "human"],
     "body/weight": ["Weight", "", "human"],
     "devices/battery": ["Battery", None, None],
     "sleep/awakeningsCount": ["Awakenings Count", "times awaken", "sleep"],
-    "sleep/efficiency": ["Sleep Efficiency", "%", "sleep"],
+    "sleep/efficiency": ["Sleep Efficiency", UNIT_PERCENTAGE, "sleep"],
     "sleep/minutesAfterWakeup": ["Minutes After Wakeup", TIME_MINUTES, "sleep"],
     "sleep/minutesAsleep": ["Sleep Minutes Asleep", TIME_MINUTES, "sleep"],
     "sleep/minutesAwake": ["Sleep Minutes Awake", TIME_MINUTES, "sleep"],
diff --git a/homeassistant/components/foobot/sensor.py b/homeassistant/components/foobot/sensor.py
index 80d17b4f23b..e0322ccbab7 100644
--- a/homeassistant/components/foobot/sensor.py
+++ b/homeassistant/components/foobot/sensor.py
@@ -17,6 +17,7 @@ from homeassistant.const import (
     CONF_USERNAME,
     TEMP_CELSIUS,
     TIME_SECONDS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.exceptions import PlatformNotReady
 from homeassistant.helpers.aiohttp_client import async_get_clientsession
@@ -37,7 +38,7 @@ SENSOR_TYPES = {
     "time": [ATTR_TIME, TIME_SECONDS],
     "pm": [ATTR_PM2_5, CONCENTRATION_MICROGRAMS_PER_CUBIC_METER, "mdi:cloud"],
     "tmp": [ATTR_TEMPERATURE, TEMP_CELSIUS, "mdi:thermometer"],
-    "hum": [ATTR_HUMIDITY, "%", "mdi:water-percent"],
+    "hum": [ATTR_HUMIDITY, UNIT_PERCENTAGE, "mdi:water-percent"],
     "co2": [
         ATTR_CARBON_DIOXIDE,
         CONCENTRATION_PARTS_PER_MILLION,
@@ -48,7 +49,7 @@ SENSOR_TYPES = {
         CONCENTRATION_PARTS_PER_BILLION,
         "mdi:cloud",
     ],
-    "allpollu": [ATTR_FOOBOT_INDEX, "%", "mdi:percent"],
+    "allpollu": [ATTR_FOOBOT_INDEX, UNIT_PERCENTAGE, "mdi:percent"],
 }
 
 SCAN_INTERVAL = timedelta(minutes=10)
diff --git a/homeassistant/components/garmin_connect/const.py b/homeassistant/components/garmin_connect/const.py
index c01f11464a1..38245ff5eb8 100644
--- a/homeassistant/components/garmin_connect/const.py
+++ b/homeassistant/components/garmin_connect/const.py
@@ -1,5 +1,5 @@
 """Constants for the Garmin Connect integration."""
-from homeassistant.const import DEVICE_CLASS_TIMESTAMP, TIME_MINUTES
+from homeassistant.const import DEVICE_CLASS_TIMESTAMP, TIME_MINUTES, UNIT_PERCENTAGE
 
 DOMAIN = "garmin_connect"
 ATTRIBUTION = "Data provided by garmin.com"
@@ -159,45 +159,51 @@ GARMIN_ENTITY_LIST = {
         None,
         True,
     ],
-    "stressPercentage": ["Stress Percentage", "%", "mdi:flash-alert", None, False],
+    "stressPercentage": [
+        "Stress Percentage",
+        UNIT_PERCENTAGE,
+        "mdi:flash-alert",
+        None,
+        False,
+    ],
     "restStressPercentage": [
         "Rest Stress Percentage",
-        "%",
+        UNIT_PERCENTAGE,
         "mdi:flash-alert",
         None,
         False,
     ],
     "activityStressPercentage": [
         "Activity Stress Percentage",
-        "%",
+        UNIT_PERCENTAGE,
         "mdi:flash-alert",
         None,
         False,
     ],
     "uncategorizedStressPercentage": [
         "Uncat. Stress Percentage",
-        "%",
+        UNIT_PERCENTAGE,
         "mdi:flash-alert",
         None,
         False,
     ],
     "lowStressPercentage": [
         "Low Stress Percentage",
-        "%",
+        UNIT_PERCENTAGE,
         "mdi:flash-alert",
         None,
         False,
     ],
     "mediumStressPercentage": [
         "Medium Stress Percentage",
-        "%",
+        UNIT_PERCENTAGE,
         "mdi:flash-alert",
         None,
         False,
     ],
     "highStressPercentage": [
         "High Stress Percentage",
-        "%",
+        UNIT_PERCENTAGE,
         "mdi:flash-alert",
         None,
         False,
@@ -225,42 +231,42 @@ GARMIN_ENTITY_LIST = {
     ],
     "bodyBatteryChargedValue": [
         "Body Battery Charged",
-        "%",
+        UNIT_PERCENTAGE,
         "mdi:battery-charging-100",
         None,
         True,
     ],
     "bodyBatteryDrainedValue": [
         "Body Battery Drained",
-        "%",
+        UNIT_PERCENTAGE,
         "mdi:battery-alert-variant-outline",
         None,
         True,
     ],
     "bodyBatteryHighestValue": [
         "Body Battery Highest",
-        "%",
+        UNIT_PERCENTAGE,
         "mdi:battery-heart",
         None,
         True,
     ],
     "bodyBatteryLowestValue": [
         "Body Battery Lowest",
-        "%",
+        UNIT_PERCENTAGE,
         "mdi:battery-heart-outline",
         None,
         True,
     ],
     "bodyBatteryMostRecentValue": [
         "Body Battery Most Recent",
-        "%",
+        UNIT_PERCENTAGE,
         "mdi:battery-positive",
         None,
         True,
     ],
-    "averageSpo2": ["Average SPO2", "%", "mdi:diabetes", None, True],
-    "lowestSpo2": ["Lowest SPO2", "%", "mdi:diabetes", None, True],
-    "latestSpo2": ["Latest SPO2", "%", "mdi:diabetes", None, True],
+    "averageSpo2": ["Average SPO2", UNIT_PERCENTAGE, "mdi:diabetes", None, True],
+    "lowestSpo2": ["Lowest SPO2", UNIT_PERCENTAGE, "mdi:diabetes", None, True],
+    "latestSpo2": ["Latest SPO2", UNIT_PERCENTAGE, "mdi:diabetes", None, True],
     "latestSpo2ReadingTimeLocal": [
         "Latest SPO2 Time",
         "",
@@ -270,7 +276,7 @@ GARMIN_ENTITY_LIST = {
     ],
     "averageMonitoringEnvironmentAltitude": [
         "Average Altitude",
-        "%",
+        UNIT_PERCENTAGE,
         "mdi:image-filter-hdr",
         None,
         False,
diff --git a/homeassistant/components/geniushub/sensor.py b/homeassistant/components/geniushub/sensor.py
index bd73c700e65..196cba7212e 100644
--- a/homeassistant/components/geniushub/sensor.py
+++ b/homeassistant/components/geniushub/sensor.py
@@ -2,7 +2,7 @@
 from datetime import timedelta
 from typing import Any, Dict
 
-from homeassistant.const import DEVICE_CLASS_BATTERY
+from homeassistant.const import DEVICE_CLASS_BATTERY, UNIT_PERCENTAGE
 from homeassistant.helpers.typing import ConfigType, HomeAssistantType
 import homeassistant.util.dt as dt_util
 
@@ -77,7 +77,7 @@ class GeniusBattery(GeniusDevice):
     @property
     def unit_of_measurement(self) -> str:
         """Return the unit of measurement of the sensor."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     @property
     def state(self) -> str:
diff --git a/homeassistant/components/glances/const.py b/homeassistant/components/glances/const.py
index 31a3f0f69e4..53dc6352049 100644
--- a/homeassistant/components/glances/const.py
+++ b/homeassistant/components/glances/const.py
@@ -1,5 +1,10 @@
 """Constants for Glances component."""
-from homeassistant.const import DATA_GIBIBYTES, DATA_MEBIBYTES, TEMP_CELSIUS
+from homeassistant.const import (
+    DATA_GIBIBYTES,
+    DATA_MEBIBYTES,
+    TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
+)
 
 DOMAIN = "glances"
 CONF_VERSION = "version"
@@ -14,13 +19,13 @@ DATA_UPDATED = "glances_data_updated"
 SUPPORTED_VERSIONS = [2, 3]
 
 SENSOR_TYPES = {
-    "disk_use_percent": ["fs", "used percent", "%", "mdi:harddisk"],
+    "disk_use_percent": ["fs", "used percent", UNIT_PERCENTAGE, "mdi:harddisk"],
     "disk_use": ["fs", "used", DATA_GIBIBYTES, "mdi:harddisk"],
     "disk_free": ["fs", "free", DATA_GIBIBYTES, "mdi:harddisk"],
-    "memory_use_percent": ["mem", "RAM used percent", "%", "mdi:memory"],
+    "memory_use_percent": ["mem", "RAM used percent", UNIT_PERCENTAGE, "mdi:memory"],
     "memory_use": ["mem", "RAM used", DATA_MEBIBYTES, "mdi:memory"],
     "memory_free": ["mem", "RAM free", DATA_MEBIBYTES, "mdi:memory"],
-    "swap_use_percent": ["memswap", "Swap used percent", "%", "mdi:memory"],
+    "swap_use_percent": ["memswap", "Swap used percent", UNIT_PERCENTAGE, "mdi:memory"],
     "swap_use": ["memswap", "Swap used", DATA_GIBIBYTES, "mdi:memory"],
     "swap_free": ["memswap", "Swap free", DATA_GIBIBYTES, "mdi:memory"],
     "processor_load": ["load", "CPU load", "15 min", "mdi:memory"],
@@ -28,10 +33,10 @@ SENSOR_TYPES = {
     "process_total": ["processcount", "Total", "Count", "mdi:memory"],
     "process_thread": ["processcount", "Thread", "Count", "mdi:memory"],
     "process_sleeping": ["processcount", "Sleeping", "Count", "mdi:memory"],
-    "cpu_use_percent": ["cpu", "CPU used", "%", "mdi:memory"],
+    "cpu_use_percent": ["cpu", "CPU used", UNIT_PERCENTAGE, "mdi:memory"],
     "sensor_temp": ["sensors", "Temp", TEMP_CELSIUS, "mdi:thermometer"],
     "docker_active": ["docker", "Containers active", "", "mdi:docker"],
-    "docker_cpu_use": ["docker", "Containers CPU used", "%", "mdi:docker"],
+    "docker_cpu_use": ["docker", "Containers CPU used", UNIT_PERCENTAGE, "mdi:docker"],
     "docker_memory_use": [
         "docker",
         "Containers RAM used",
diff --git a/homeassistant/components/history_stats/sensor.py b/homeassistant/components/history_stats/sensor.py
index 0b1289ab05f..48d65145219 100644
--- a/homeassistant/components/history_stats/sensor.py
+++ b/homeassistant/components/history_stats/sensor.py
@@ -14,6 +14,7 @@ from homeassistant.const import (
     CONF_TYPE,
     EVENT_HOMEASSISTANT_START,
     TIME_HOURS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import callback
 from homeassistant.exceptions import TemplateError
@@ -36,7 +37,11 @@ CONF_TYPE_COUNT = "count"
 CONF_TYPE_KEYS = [CONF_TYPE_TIME, CONF_TYPE_RATIO, CONF_TYPE_COUNT]
 
 DEFAULT_NAME = "unnamed statistics"
-UNITS = {CONF_TYPE_TIME: TIME_HOURS, CONF_TYPE_RATIO: "%", CONF_TYPE_COUNT: ""}
+UNITS = {
+    CONF_TYPE_TIME: TIME_HOURS,
+    CONF_TYPE_RATIO: UNIT_PERCENTAGE,
+    CONF_TYPE_COUNT: "",
+}
 ICON = "mdi:chart-line"
 
 ATTR_VALUE = "value"
diff --git a/homeassistant/components/homekit/__init__.py b/homeassistant/components/homekit/__init__.py
index ca5a601068a..c46bd754319 100644
--- a/homeassistant/components/homekit/__init__.py
+++ b/homeassistant/components/homekit/__init__.py
@@ -23,6 +23,7 @@ from homeassistant.const import (
     EVENT_HOMEASSISTANT_STOP,
     TEMP_CELSIUS,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entityfilter import FILTER_SCHEMA
@@ -236,7 +237,7 @@ def get_accessory(hass, driver, state, aid, config):
             TEMP_FAHRENHEIT,
         ):
             a_type = "TemperatureSensor"
-        elif device_class == DEVICE_CLASS_HUMIDITY and unit == "%":
+        elif device_class == DEVICE_CLASS_HUMIDITY and unit == UNIT_PERCENTAGE:
             a_type = "HumiditySensor"
         elif device_class == DEVICE_CLASS_PM25 or DEVICE_CLASS_PM25 in state.entity_id:
             a_type = "AirQualitySensor"
diff --git a/homeassistant/components/homekit_controller/sensor.py b/homeassistant/components/homekit_controller/sensor.py
index ab8a6fa6672..636c10dbe79 100644
--- a/homeassistant/components/homekit_controller/sensor.py
+++ b/homeassistant/components/homekit_controller/sensor.py
@@ -8,6 +8,7 @@ from homeassistant.const import (
     DEVICE_CLASS_ILLUMINANCE,
     DEVICE_CLASS_TEMPERATURE,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import callback
 
@@ -18,7 +19,6 @@ TEMP_C_ICON = "mdi:thermometer"
 BRIGHTNESS_ICON = "mdi:brightness-6"
 CO2_ICON = "mdi:periodic-table-co2"
 
-UNIT_PERCENT = "%"
 UNIT_LUX = "lux"
 
 
@@ -52,7 +52,7 @@ class HomeKitHumiditySensor(HomeKitEntity):
     @property
     def unit_of_measurement(self):
         """Return units for the sensor."""
-        return UNIT_PERCENT
+        return UNIT_PERCENTAGE
 
     def _update_relative_humidity_current(self, value):
         self._state = value
@@ -234,7 +234,7 @@ class HomeKitBatterySensor(HomeKitEntity):
     @property
     def unit_of_measurement(self):
         """Return units for the sensor."""
-        return UNIT_PERCENT
+        return UNIT_PERCENTAGE
 
     def _update_battery_level(self, value):
         self._state = value
diff --git a/homeassistant/components/homematic/sensor.py b/homeassistant/components/homematic/sensor.py
index 09d1e2f59cf..e8b97477546 100644
--- a/homeassistant/components/homematic/sensor.py
+++ b/homeassistant/components/homematic/sensor.py
@@ -9,6 +9,7 @@ from homeassistant.const import (
     ENERGY_WATT_HOUR,
     POWER_WATT,
     SPEED_KILOMETERS_PER_HOUR,
+    UNIT_PERCENTAGE,
     VOLUME_CUBIC_METERS,
 )
 
@@ -32,7 +33,7 @@ HM_STATE_HA_CAST = {
 }
 
 HM_UNIT_HA_CAST = {
-    "HUMIDITY": "%",
+    "HUMIDITY": UNIT_PERCENTAGE,
     "TEMPERATURE": "°C",
     "ACTUAL_TEMPERATURE": "°C",
     "BRIGHTNESS": "#",
diff --git a/homeassistant/components/homematicip_cloud/sensor.py b/homeassistant/components/homematicip_cloud/sensor.py
index 4335eebb8b8..a45591ecc30 100644
--- a/homeassistant/components/homematicip_cloud/sensor.py
+++ b/homeassistant/components/homematicip_cloud/sensor.py
@@ -33,6 +33,7 @@ from homeassistant.const import (
     POWER_WATT,
     SPEED_KILOMETERS_PER_HOUR,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.typing import HomeAssistantType
 
@@ -155,7 +156,7 @@ class HomematicipAccesspointStatus(HomematicipGenericDevice):
     @property
     def unit_of_measurement(self) -> str:
         """Return the unit this state is expressed in."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     @property
     def device_state_attributes(self) -> Dict[str, Any]:
@@ -194,7 +195,7 @@ class HomematicipHeatingThermostat(HomematicipGenericDevice):
     @property
     def unit_of_measurement(self) -> str:
         """Return the unit this state is expressed in."""
-        return "%"
+        return UNIT_PERCENTAGE
 
 
 class HomematicipHumiditySensor(HomematicipGenericDevice):
@@ -217,7 +218,7 @@ class HomematicipHumiditySensor(HomematicipGenericDevice):
     @property
     def unit_of_measurement(self) -> str:
         """Return the unit this state is expressed in."""
-        return "%"
+        return UNIT_PERCENTAGE
 
 
 class HomematicipTemperatureSensor(HomematicipGenericDevice):
diff --git a/homeassistant/components/htu21d/sensor.py b/homeassistant/components/htu21d/sensor.py
index 954ba60abbf..5bd77d4dcb2 100644
--- a/homeassistant/components/htu21d/sensor.py
+++ b/homeassistant/components/htu21d/sensor.py
@@ -8,7 +8,7 @@ import smbus  # pylint: disable=import-error
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_NAME, TEMP_FAHRENHEIT
+from homeassistant.const import CONF_NAME, TEMP_FAHRENHEIT, UNIT_PERCENTAGE
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 from homeassistant.util import Throttle
@@ -50,7 +50,7 @@ async def async_setup_platform(hass, config, async_add_entities, discovery_info=
 
     dev = [
         HTU21DSensor(sensor_handler, name, SENSOR_TEMPERATURE, temp_unit),
-        HTU21DSensor(sensor_handler, name, SENSOR_HUMIDITY, "%"),
+        HTU21DSensor(sensor_handler, name, SENSOR_HUMIDITY, UNIT_PERCENTAGE),
     ]
 
     async_add_entities(dev)
diff --git a/homeassistant/components/icloud/sensor.py b/homeassistant/components/icloud/sensor.py
index e24016795d3..5438b9ce810 100644
--- a/homeassistant/components/icloud/sensor.py
+++ b/homeassistant/components/icloud/sensor.py
@@ -3,7 +3,7 @@ import logging
 from typing import Dict
 
 from homeassistant.config_entries import ConfigEntry
-from homeassistant.const import CONF_USERNAME, DEVICE_CLASS_BATTERY
+from homeassistant.const import CONF_USERNAME, DEVICE_CLASS_BATTERY, UNIT_PERCENTAGE
 from homeassistant.helpers.dispatcher import async_dispatcher_connect
 from homeassistant.helpers.entity import Entity
 from homeassistant.helpers.icon import icon_for_battery_level
@@ -61,7 +61,7 @@ class IcloudDeviceBatterySensor(Entity):
     @property
     def unit_of_measurement(self) -> str:
         """Battery state measured in percentage."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     @property
     def icon(self) -> str:
diff --git a/homeassistant/components/ios/sensor.py b/homeassistant/components/ios/sensor.py
index 85a0a81fdf3..e12ab9b4a40 100644
--- a/homeassistant/components/ios/sensor.py
+++ b/homeassistant/components/ios/sensor.py
@@ -1,9 +1,13 @@
 """Support for Home Assistant iOS app sensors."""
 from homeassistant.components import ios
+from homeassistant.const import UNIT_PERCENTAGE
 from homeassistant.helpers.entity import Entity
 from homeassistant.helpers.icon import icon_for_battery_level
 
-SENSOR_TYPES = {"level": ["Battery Level", "%"], "state": ["Battery State", None]}
+SENSOR_TYPES = {
+    "level": ["Battery Level", UNIT_PERCENTAGE],
+    "state": ["Battery State", None],
+}
 
 DEFAULT_ICON_LEVEL = "mdi:battery"
 DEFAULT_ICON_STATE = "mdi:power-plug"
diff --git a/homeassistant/components/isy994/__init__.py b/homeassistant/components/isy994/__init__.py
index 3cffbdb1214..6615fc6c569 100644
--- a/homeassistant/components/isy994/__init__.py
+++ b/homeassistant/components/isy994/__init__.py
@@ -12,6 +12,7 @@ from homeassistant.const import (
     CONF_PASSWORD,
     CONF_USERNAME,
     EVENT_HOMEASSISTANT_STOP,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import HomeAssistant
 from homeassistant.helpers import config_validation as cv, discovery
@@ -101,7 +102,7 @@ NODE_FILTERS = {
     },
     "light": {
         "uom": ["51"],
-        "states": ["on", "off", "%"],
+        "states": ["on", "off", UNIT_PERCENTAGE],
         "node_def_id": [
             "DimmerLampSwitch",
             "DimmerLampSwitch_ADV",
diff --git a/homeassistant/components/isy994/sensor.py b/homeassistant/components/isy994/sensor.py
index 42590b0ea13..9e2f3e90957 100644
--- a/homeassistant/components/isy994/sensor.py
+++ b/homeassistant/components/isy994/sensor.py
@@ -18,6 +18,7 @@ from homeassistant.const import (
     TIME_MONTHS,
     TIME_SECONDS,
     TIME_YEARS,
+    UNIT_PERCENTAGE,
     UNIT_UV_INDEX,
 )
 from homeassistant.helpers.typing import ConfigType
@@ -74,7 +75,7 @@ UOM_FRIENDLY_NAME = {
     "48": SPEED_MILES_PER_HOUR,
     "49": SPEED_METERS_PER_SECOND,
     "50": "ohm",
-    "51": "%",
+    "51": UNIT_PERCENTAGE,
     "52": "lb",
     "53": "power factor",
     "54": CONCENTRATION_PARTS_PER_MILLION,
diff --git a/homeassistant/components/kaiterra/const.py b/homeassistant/components/kaiterra/const.py
index 6c3ea4d6f01..7f7eff99444 100644
--- a/homeassistant/components/kaiterra/const.py
+++ b/homeassistant/components/kaiterra/const.py
@@ -7,6 +7,7 @@ from homeassistant.const import (
     CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
     CONCENTRATION_PARTS_PER_BILLION,
     CONCENTRATION_PARTS_PER_MILLION,
+    UNIT_PERCENTAGE,
 )
 
 DOMAIN = "kaiterra"
@@ -53,7 +54,7 @@ ATTR_AQI_POLLUTANT = "air_quality_index_pollutant"
 AVAILABLE_AQI_STANDARDS = ["us", "cn", "in"]
 AVAILABLE_UNITS = [
     "x",
-    "%",
+    UNIT_PERCENTAGE,
     "C",
     "F",
     CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
diff --git a/homeassistant/components/konnected/sensor.py b/homeassistant/components/konnected/sensor.py
index 4fa238166f8..e936898d7fb 100644
--- a/homeassistant/components/konnected/sensor.py
+++ b/homeassistant/components/konnected/sensor.py
@@ -10,6 +10,7 @@ from homeassistant.const import (
     DEVICE_CLASS_HUMIDITY,
     DEVICE_CLASS_TEMPERATURE,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import callback
 from homeassistant.helpers.dispatcher import async_dispatcher_connect
@@ -21,7 +22,7 @@ _LOGGER = logging.getLogger(__name__)
 
 SENSOR_TYPES = {
     DEVICE_CLASS_TEMPERATURE: ["Temperature", TEMP_CELSIUS],
-    DEVICE_CLASS_HUMIDITY: ["Humidity", "%"],
+    DEVICE_CLASS_HUMIDITY: ["Humidity", UNIT_PERCENTAGE],
 }
 
 
@@ -119,9 +120,7 @@ class KonnectedSensor(Entity):
     @property
     def device_info(self):
         """Return the device info."""
-        return {
-            "identifiers": {(KONNECTED_DOMAIN, self._device_id)},
-        }
+        return {"identifiers": {(KONNECTED_DOMAIN, self._device_id)}}
 
     async def async_added_to_hass(self):
         """Store entity_id and register state change callback."""
diff --git a/homeassistant/components/lacrosse/sensor.py b/homeassistant/components/lacrosse/sensor.py
index b8bde797b39..1d38764710a 100644
--- a/homeassistant/components/lacrosse/sensor.py
+++ b/homeassistant/components/lacrosse/sensor.py
@@ -15,6 +15,7 @@ from homeassistant.const import (
     CONF_TYPE,
     EVENT_HOMEASSISTANT_STOP,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import callback
 import homeassistant.helpers.config_validation as cv
@@ -193,7 +194,7 @@ class LaCrosseHumidity(LaCrosseSensor):
     @property
     def unit_of_measurement(self):
         """Return the unit of measurement."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     @property
     def state(self):
diff --git a/homeassistant/components/lcn/const.py b/homeassistant/components/lcn/const.py
index ff7de1987da..0a46190fbf9 100644
--- a/homeassistant/components/lcn/const.py
+++ b/homeassistant/components/lcn/const.py
@@ -1,7 +1,7 @@
 """Constants for the LCN component."""
 from itertools import product
 
-from homeassistant.const import TEMP_CELSIUS, TEMP_FAHRENHEIT
+from homeassistant.const import TEMP_CELSIUS, TEMP_FAHRENHEIT, UNIT_PERCENTAGE
 
 DOMAIN = "lcn"
 DATA_LCN = "lcn"
@@ -153,7 +153,7 @@ VAR_UNITS = [
     "LX",
     "M/S",
     "METERPERSECOND",
-    "%",
+    UNIT_PERCENTAGE,
     "PERCENT",
     "PPM",
     "VOLT",
diff --git a/homeassistant/components/linux_battery/sensor.py b/homeassistant/components/linux_battery/sensor.py
index bc02affdaed..bb1dd34dc00 100644
--- a/homeassistant/components/linux_battery/sensor.py
+++ b/homeassistant/components/linux_battery/sensor.py
@@ -6,7 +6,12 @@ from batinfo import Batteries
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import ATTR_NAME, CONF_NAME, DEVICE_CLASS_BATTERY
+from homeassistant.const import (
+    ATTR_NAME,
+    CONF_NAME,
+    DEVICE_CLASS_BATTERY,
+    UNIT_PERCENTAGE,
+)
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 
@@ -98,7 +103,7 @@ class LinuxBatterySensor(Entity):
     @property
     def unit_of_measurement(self):
         """Return the unit the value is expressed in."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     @property
     def device_state_attributes(self):
diff --git a/homeassistant/components/logi_circle/const.py b/homeassistant/components/logi_circle/const.py
index 4be4823f8d7..333a85e9b77 100644
--- a/homeassistant/components/logi_circle/const.py
+++ b/homeassistant/components/logi_circle/const.py
@@ -1,4 +1,5 @@
 """Constants in Logi Circle component."""
+from homeassistant.const import UNIT_PERCENTAGE
 
 CONF_CLIENT_ID = "client_id"
 CONF_CLIENT_SECRET = "client_secret"
@@ -15,11 +16,11 @@ RECORDING_MODE_KEY = "RECORDING_MODE"
 
 # Sensor types: Name, unit of measure, icon per sensor key.
 LOGI_SENSORS = {
-    "battery_level": ["Battery", "%", "battery-50"],
+    "battery_level": ["Battery", UNIT_PERCENTAGE, "battery-50"],
     "last_activity_time": ["Last Activity", None, "history"],
     "recording": ["Recording Mode", None, "eye"],
     "signal_strength_category": ["WiFi Signal Category", None, "wifi"],
-    "signal_strength_percentage": ["WiFi Signal Strength", "%", "wifi"],
+    "signal_strength_percentage": ["WiFi Signal Strength", UNIT_PERCENTAGE, "wifi"],
     "streaming": ["Streaming Mode", None, "camera"],
 }
 
diff --git a/homeassistant/components/luftdaten/__init__.py b/homeassistant/components/luftdaten/__init__.py
index a722829a4a2..f7ed2d72f16 100644
--- a/homeassistant/components/luftdaten/__init__.py
+++ b/homeassistant/components/luftdaten/__init__.py
@@ -13,6 +13,7 @@ from homeassistant.const import (
     CONF_SENSORS,
     CONF_SHOW_ON_MAP,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import callback
 from homeassistant.exceptions import ConfigEntryNotReady
@@ -42,7 +43,7 @@ TOPIC_UPDATE = f"{DOMAIN}_data_update"
 
 SENSORS = {
     SENSOR_TEMPERATURE: ["Temperature", "mdi:thermometer", TEMP_CELSIUS],
-    SENSOR_HUMIDITY: ["Humidity", "mdi:water-percent", "%"],
+    SENSOR_HUMIDITY: ["Humidity", "mdi:water-percent", UNIT_PERCENTAGE],
     SENSOR_PRESSURE: ["Pressure", "mdi:arrow-down-bold", "Pa"],
     SENSOR_PRESSURE_AT_SEALEVEL: ["Pressure at sealevel", "mdi:download", "Pa"],
     SENSOR_PM10: [
diff --git a/homeassistant/components/meteo_france/const.py b/homeassistant/components/meteo_france/const.py
index 9fde6f38b51..b7647f5d97b 100644
--- a/homeassistant/components/meteo_france/const.py
+++ b/homeassistant/components/meteo_france/const.py
@@ -1,6 +1,11 @@
 """Meteo-France component constants."""
 
-from homeassistant.const import SPEED_KILOMETERS_PER_HOUR, TEMP_CELSIUS, TIME_MINUTES
+from homeassistant.const import (
+    SPEED_KILOMETERS_PER_HOUR,
+    TEMP_CELSIUS,
+    TIME_MINUTES,
+    UNIT_PERCENTAGE,
+)
 
 DOMAIN = "meteo_france"
 PLATFORMS = ["sensor", "weather"]
@@ -17,25 +22,25 @@ SENSOR_TYPE_CLASS = "device_class"
 SENSOR_TYPES = {
     "rain_chance": {
         SENSOR_TYPE_NAME: "Rain chance",
-        SENSOR_TYPE_UNIT: "%",
+        SENSOR_TYPE_UNIT: UNIT_PERCENTAGE,
         SENSOR_TYPE_ICON: "mdi:weather-rainy",
         SENSOR_TYPE_CLASS: None,
     },
     "freeze_chance": {
         SENSOR_TYPE_NAME: "Freeze chance",
-        SENSOR_TYPE_UNIT: "%",
+        SENSOR_TYPE_UNIT: UNIT_PERCENTAGE,
         SENSOR_TYPE_ICON: "mdi:snowflake",
         SENSOR_TYPE_CLASS: None,
     },
     "thunder_chance": {
         SENSOR_TYPE_NAME: "Thunder chance",
-        SENSOR_TYPE_UNIT: "%",
+        SENSOR_TYPE_UNIT: UNIT_PERCENTAGE,
         SENSOR_TYPE_ICON: "mdi:weather-lightning",
         SENSOR_TYPE_CLASS: None,
     },
     "snow_chance": {
         SENSOR_TYPE_NAME: "Snow chance",
-        SENSOR_TYPE_UNIT: "%",
+        SENSOR_TYPE_UNIT: UNIT_PERCENTAGE,
         SENSOR_TYPE_ICON: "mdi:weather-snowy",
         SENSOR_TYPE_CLASS: None,
     },
diff --git a/homeassistant/components/metoffice/sensor.py b/homeassistant/components/metoffice/sensor.py
index 6e6fde06d8c..1c4ca83e5bd 100644
--- a/homeassistant/components/metoffice/sensor.py
+++ b/homeassistant/components/metoffice/sensor.py
@@ -15,6 +15,7 @@ from homeassistant.const import (
     CONF_NAME,
     SPEED_MILES_PER_HOUR,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -71,8 +72,8 @@ SENSOR_TYPES = {
     "visibility": ["Visibility", None],
     "visibility_distance": ["Visibility Distance", "km"],
     "uv": ["UV", None],
-    "precipitation": ["Probability of Precipitation", "%"],
-    "humidity": ["Humidity", "%"],
+    "precipitation": ["Probability of Precipitation", UNIT_PERCENTAGE],
+    "humidity": ["Humidity", UNIT_PERCENTAGE],
 }
 
 PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend(
diff --git a/homeassistant/components/microsoft/tts.py b/homeassistant/components/microsoft/tts.py
index 074605e07fe..c857cc731f4 100644
--- a/homeassistant/components/microsoft/tts.py
+++ b/homeassistant/components/microsoft/tts.py
@@ -6,7 +6,7 @@ from pycsspeechtts import pycsspeechtts
 import voluptuous as vol
 
 from homeassistant.components.tts import CONF_LANG, PLATFORM_SCHEMA, Provider
-from homeassistant.const import CONF_API_KEY, CONF_TYPE
+from homeassistant.const import CONF_API_KEY, CONF_TYPE, UNIT_PERCENTAGE
 import homeassistant.helpers.config_validation as cv
 
 CONF_GENDER = "gender"
@@ -122,8 +122,8 @@ class MicrosoftProvider(Provider):
         self._gender = gender
         self._type = ttype
         self._output = DEFAULT_OUTPUT
-        self._rate = f"{rate}%"
-        self._volume = f"{volume}%"
+        self._rate = f"{rate}{UNIT_PERCENTAGE}"
+        self._volume = f"{volume}{UNIT_PERCENTAGE}"
         self._pitch = pitch
         self._contour = contour
         self._region = region
diff --git a/homeassistant/components/miflora/sensor.py b/homeassistant/components/miflora/sensor.py
index 815a6e97bb8..bd551517562 100644
--- a/homeassistant/components/miflora/sensor.py
+++ b/homeassistant/components/miflora/sensor.py
@@ -15,6 +15,7 @@ from homeassistant.const import (
     CONF_NAME,
     CONF_SCAN_INTERVAL,
     EVENT_HOMEASSISTANT_START,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import callback
 import homeassistant.helpers.config_validation as cv
@@ -43,9 +44,9 @@ SCAN_INTERVAL = timedelta(seconds=1200)
 SENSOR_TYPES = {
     "temperature": ["Temperature", "°C", "mdi:thermometer"],
     "light": ["Light intensity", "lx", "mdi:white-balance-sunny"],
-    "moisture": ["Moisture", "%", "mdi:water-percent"],
+    "moisture": ["Moisture", UNIT_PERCENTAGE, "mdi:water-percent"],
     "conductivity": ["Conductivity", "µS/cm", "mdi:flash-circle"],
-    "battery": ["Battery", "%", "mdi:battery-charging"],
+    "battery": ["Battery", UNIT_PERCENTAGE, "mdi:battery-charging"],
 }
 
 PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend(
diff --git a/homeassistant/components/mitemp_bt/sensor.py b/homeassistant/components/mitemp_bt/sensor.py
index b536149680d..febfb93cf1d 100644
--- a/homeassistant/components/mitemp_bt/sensor.py
+++ b/homeassistant/components/mitemp_bt/sensor.py
@@ -15,6 +15,7 @@ from homeassistant.const import (
     DEVICE_CLASS_BATTERY,
     DEVICE_CLASS_HUMIDITY,
     DEVICE_CLASS_TEMPERATURE,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -46,8 +47,8 @@ DEFAULT_TIMEOUT = 10
 # Sensor types are defined like: Name, units
 SENSOR_TYPES = {
     "temperature": [DEVICE_CLASS_TEMPERATURE, "Temperature", "°C"],
-    "humidity": [DEVICE_CLASS_HUMIDITY, "Humidity", "%"],
-    "battery": [DEVICE_CLASS_BATTERY, "Battery", "%"],
+    "humidity": [DEVICE_CLASS_HUMIDITY, "Humidity", UNIT_PERCENTAGE],
+    "battery": [DEVICE_CLASS_BATTERY, "Battery", UNIT_PERCENTAGE],
 }
 
 PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend(
diff --git a/homeassistant/components/mold_indicator/sensor.py b/homeassistant/components/mold_indicator/sensor.py
index 0d6c6f55284..b5c72fdce29 100644
--- a/homeassistant/components/mold_indicator/sensor.py
+++ b/homeassistant/components/mold_indicator/sensor.py
@@ -13,6 +13,7 @@ from homeassistant.const import (
     STATE_UNKNOWN,
     TEMP_CELSIUS,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import callback
 import homeassistant.helpers.config_validation as cv
@@ -245,7 +246,7 @@ class MoldIndicator(Entity):
             )
             return None
 
-        if unit != "%":
+        if unit != UNIT_PERCENTAGE:
             _LOGGER.error(
                 "Humidity sensor %s has unsupported unit: %s %s",
                 state.entity_id,
@@ -360,7 +361,7 @@ class MoldIndicator(Entity):
     @property
     def unit_of_measurement(self):
         """Return the unit of measurement."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     @property
     def state(self):
diff --git a/homeassistant/components/mychevy/sensor.py b/homeassistant/components/mychevy/sensor.py
index 844c301fe49..56335bb1650 100644
--- a/homeassistant/components/mychevy/sensor.py
+++ b/homeassistant/components/mychevy/sensor.py
@@ -2,6 +2,7 @@
 import logging
 
 from homeassistant.components.sensor import ENTITY_ID_FORMAT
+from homeassistant.const import UNIT_PERCENTAGE
 from homeassistant.core import callback
 from homeassistant.helpers.entity import Entity
 from homeassistant.helpers.icon import icon_for_battery_level
@@ -25,7 +26,9 @@ SENSORS = [
     EVSensorConfig("Electric Range", "electricRange", "miles", "mdi:speedometer"),
     EVSensorConfig("Charged By", "estimatedFullChargeBy"),
     EVSensorConfig("Charge Mode", "chargeMode"),
-    EVSensorConfig("Battery Level", BATTERY_SENSOR, "%", "mdi:battery", ["charging"]),
+    EVSensorConfig(
+        "Battery Level", BATTERY_SENSOR, UNIT_PERCENTAGE, "mdi:battery", ["charging"]
+    ),
 ]
 
 
diff --git a/homeassistant/components/mysensors/sensor.py b/homeassistant/components/mysensors/sensor.py
index 2b8cf208c14..997728ed495 100644
--- a/homeassistant/components/mysensors/sensor.py
+++ b/homeassistant/components/mysensors/sensor.py
@@ -7,13 +7,14 @@ from homeassistant.const import (
     POWER_WATT,
     TEMP_CELSIUS,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 
 SENSORS = {
     "V_TEMP": [None, "mdi:thermometer"],
-    "V_HUM": ["%", "mdi:water-percent"],
-    "V_DIMMER": ["%", "mdi:percent"],
-    "V_PERCENTAGE": ["%", "mdi:percent"],
+    "V_HUM": [UNIT_PERCENTAGE, "mdi:water-percent"],
+    "V_DIMMER": [UNIT_PERCENTAGE, "mdi:percent"],
+    "V_PERCENTAGE": [UNIT_PERCENTAGE, "mdi:percent"],
     "V_PRESSURE": [None, "mdi:gauge"],
     "V_FORECAST": [None, "mdi:weather-partly-cloudy"],
     "V_RAIN": [None, "mdi:weather-rainy"],
@@ -26,7 +27,7 @@ SENSORS = {
     "V_IMPEDANCE": ["ohm", None],
     "V_WATT": [POWER_WATT, None],
     "V_KWH": [ENERGY_KILO_WATT_HOUR, None],
-    "V_LIGHT_LEVEL": ["%", "mdi:white-balance-sunny"],
+    "V_LIGHT_LEVEL": [UNIT_PERCENTAGE, "mdi:white-balance-sunny"],
     "V_FLOW": ["m", "mdi:gauge"],
     "V_VOLUME": ["m³", None],
     "V_LEVEL": {
diff --git a/homeassistant/components/neato/sensor.py b/homeassistant/components/neato/sensor.py
index 70d273fe690..5573e280a99 100644
--- a/homeassistant/components/neato/sensor.py
+++ b/homeassistant/components/neato/sensor.py
@@ -5,6 +5,7 @@ import logging
 from pybotvac.exceptions import NeatoRobotException
 
 from homeassistant.components.sensor import DEVICE_CLASS_BATTERY
+from homeassistant.const import UNIT_PERCENTAGE
 from homeassistant.helpers.entity import Entity
 
 from .const import NEATO_DOMAIN, NEATO_LOGIN, NEATO_ROBOTS, SCAN_INTERVAL_MINUTES
@@ -83,7 +84,7 @@ class NeatoSensor(Entity):
     @property
     def unit_of_measurement(self):
         """Return unit of measurement."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     @property
     def device_info(self):
diff --git a/homeassistant/components/nest/sensor.py b/homeassistant/components/nest/sensor.py
index d52df4c6586..225caee0a90 100644
--- a/homeassistant/components/nest/sensor.py
+++ b/homeassistant/components/nest/sensor.py
@@ -8,6 +8,7 @@ from homeassistant.const import (
     STATE_OFF,
     TEMP_CELSIUS,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 
 from . import CONF_SENSORS, DATA_NEST, DATA_NEST_CONFIG, NestSensorDevice
@@ -41,7 +42,7 @@ _VALID_SENSOR_TYPES = (
     + STRUCTURE_CAMERA_SENSOR_TYPES
 )
 
-SENSOR_UNITS = {"humidity": "%"}
+SENSOR_UNITS = {"humidity": UNIT_PERCENTAGE}
 
 SENSOR_DEVICE_CLASSES = {"humidity": DEVICE_CLASS_HUMIDITY}
 
diff --git a/homeassistant/components/netatmo/sensor.py b/homeassistant/components/netatmo/sensor.py
index 9254f2f45ab..f52b6797a7a 100644
--- a/homeassistant/components/netatmo/sensor.py
+++ b/homeassistant/components/netatmo/sensor.py
@@ -11,6 +11,7 @@ from homeassistant.const import (
     DEVICE_CLASS_TEMPERATURE,
     SPEED_KILOMETERS_PER_HOUR,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.entity import Entity
 from homeassistant.util import Throttle
@@ -57,13 +58,18 @@ SENSOR_TYPES = {
     "co2": ["CO2", CONCENTRATION_PARTS_PER_MILLION, "mdi:periodic-table-co2", None],
     "pressure": ["Pressure", "mbar", "mdi:gauge", None],
     "noise": ["Noise", "dB", "mdi:volume-high", None],
-    "humidity": ["Humidity", "%", "mdi:water-percent", DEVICE_CLASS_HUMIDITY],
+    "humidity": [
+        "Humidity",
+        UNIT_PERCENTAGE,
+        "mdi:water-percent",
+        DEVICE_CLASS_HUMIDITY,
+    ],
     "rain": ["Rain", "mm", "mdi:weather-rainy", None],
     "sum_rain_1": ["sum_rain_1", "mm", "mdi:weather-rainy", None],
     "sum_rain_24": ["sum_rain_24", "mm", "mdi:weather-rainy", None],
     "battery_vp": ["Battery", "", "mdi:battery", None],
     "battery_lvl": ["Battery_lvl", "", "mdi:battery", None],
-    "battery_percent": ["battery_percent", "%", None, DEVICE_CLASS_BATTERY],
+    "battery_percent": ["battery_percent", UNIT_PERCENTAGE, None, DEVICE_CLASS_BATTERY],
     "min_temp": ["Min Temp.", TEMP_CELSIUS, "mdi:thermometer", None],
     "max_temp": ["Max Temp.", TEMP_CELSIUS, "mdi:thermometer", None],
     "windangle": ["Angle", "", "mdi:compass", None],
diff --git a/homeassistant/components/netdata/sensor.py b/homeassistant/components/netdata/sensor.py
index edabef9535c..4406734b094 100644
--- a/homeassistant/components/netdata/sensor.py
+++ b/homeassistant/components/netdata/sensor.py
@@ -13,6 +13,7 @@ from homeassistant.const import (
     CONF_NAME,
     CONF_PORT,
     CONF_RESOURCES,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.exceptions import PlatformNotReady
 from homeassistant.helpers.aiohttp_client import async_get_clientsession
@@ -78,7 +79,7 @@ async def async_setup_platform(hass, config, async_add_entities, discovery_info=
         try:
             resource_data = netdata.api.metrics[sensor]
             unit = (
-                "%"
+                UNIT_PERCENTAGE
                 if resource_data["units"] == "percentage"
                 else resource_data["units"]
             )
diff --git a/homeassistant/components/netgear_lte/sensor_types.py b/homeassistant/components/netgear_lte/sensor_types.py
index a744937dacd..883b4803544 100644
--- a/homeassistant/components/netgear_lte/sensor_types.py
+++ b/homeassistant/components/netgear_lte/sensor_types.py
@@ -1,7 +1,7 @@
 """Define possible sensor types."""
 
 from homeassistant.components.binary_sensor import DEVICE_CLASS_CONNECTIVITY
-from homeassistant.const import DATA_MEBIBYTES
+from homeassistant.const import DATA_MEBIBYTES, UNIT_PERCENTAGE
 
 SENSOR_SMS = "sms"
 SENSOR_SMS_TOTAL = "sms_total"
@@ -11,7 +11,7 @@ SENSOR_UNITS = {
     SENSOR_SMS: "unread",
     SENSOR_SMS_TOTAL: "messages",
     SENSOR_USAGE: DATA_MEBIBYTES,
-    "radio_quality": "%",
+    "radio_quality": UNIT_PERCENTAGE,
     "rx_level": "dBm",
     "tx_level": "dBm",
     "upstream": None,
diff --git a/homeassistant/components/nfandroidtv/notify.py b/homeassistant/components/nfandroidtv/notify.py
index 52f0af607bc..280733affd2 100644
--- a/homeassistant/components/nfandroidtv/notify.py
+++ b/homeassistant/components/nfandroidtv/notify.py
@@ -14,7 +14,7 @@ from homeassistant.components.notify import (
     PLATFORM_SCHEMA,
     BaseNotificationService,
 )
-from homeassistant.const import CONF_HOST, CONF_TIMEOUT
+from homeassistant.const import CONF_HOST, CONF_TIMEOUT, UNIT_PERCENTAGE
 import homeassistant.helpers.config_validation as cv
 
 _LOGGER = logging.getLogger(__name__)
@@ -66,7 +66,14 @@ POSITIONS = {
     "center": 4,
 }
 
-TRANSPARENCIES = {"default": 0, "0%": 1, "25%": 2, "50%": 3, "75%": 4, "100%": 5}
+TRANSPARENCIES = {
+    "default": 0,
+    f"0{UNIT_PERCENTAGE}": 1,
+    f"25{UNIT_PERCENTAGE}": 2,
+    f"50{UNIT_PERCENTAGE}": 3,
+    f"75{UNIT_PERCENTAGE}": 4,
+    f"100{UNIT_PERCENTAGE}": 5,
+}
 
 COLORS = {
     "grey": "#607d8b",
diff --git a/homeassistant/components/nissan_leaf/sensor.py b/homeassistant/components/nissan_leaf/sensor.py
index bbdb8ad7527..33b0efa5d60 100644
--- a/homeassistant/components/nissan_leaf/sensor.py
+++ b/homeassistant/components/nissan_leaf/sensor.py
@@ -1,7 +1,7 @@
 """Battery Charge and Range Support for the Nissan Leaf."""
 import logging
 
-from homeassistant.const import DEVICE_CLASS_BATTERY
+from homeassistant.const import DEVICE_CLASS_BATTERY, UNIT_PERCENTAGE
 from homeassistant.helpers.icon import icon_for_battery_level
 from homeassistant.util.distance import LENGTH_KILOMETERS, LENGTH_MILES
 from homeassistant.util.unit_system import IMPERIAL_SYSTEM, METRIC_SYSTEM
@@ -56,7 +56,7 @@ class LeafBatterySensor(LeafEntity):
     @property
     def unit_of_measurement(self):
         """Battery state measured in percentage."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     @property
     def icon(self):
diff --git a/homeassistant/components/nut/sensor.py b/homeassistant/components/nut/sensor.py
index 96db220f5ea..15dee84dd9b 100644
--- a/homeassistant/components/nut/sensor.py
+++ b/homeassistant/components/nut/sensor.py
@@ -19,6 +19,7 @@ from homeassistant.const import (
     STATE_UNKNOWN,
     TEMP_CELSIUS,
     TIME_SECONDS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.exceptions import PlatformNotReady
 import homeassistant.helpers.config_validation as cv
@@ -51,8 +52,8 @@ SENSOR_TYPES = {
     "ups.firmware": ["Firmware Version", "", "mdi:information-outline"],
     "ups.firmware.aux": ["Firmware Version 2", "", "mdi:information-outline"],
     "ups.temperature": ["UPS Temperature", TEMP_CELSIUS, "mdi:thermometer"],
-    "ups.load": ["Load", "%", "mdi:gauge"],
-    "ups.load.high": ["Overload Setting", "%", "mdi:gauge"],
+    "ups.load": ["Load", UNIT_PERCENTAGE, "mdi:gauge"],
+    "ups.load.high": ["Overload Setting", UNIT_PERCENTAGE, "mdi:gauge"],
     "ups.id": ["System identifier", "", "mdi:information-outline"],
     "ups.delay.start": ["Load Restart Delay", TIME_SECONDS, "mdi:timer"],
     "ups.delay.reboot": ["UPS Reboot Delay", TIME_SECONDS, "mdi:timer"],
@@ -65,7 +66,7 @@ SENSOR_TYPES = {
     "ups.test.date": ["Self-Test Date", "", "mdi:calendar"],
     "ups.display.language": ["Language", "", "mdi:information-outline"],
     "ups.contacts": ["External Contacts", "", "mdi:information-outline"],
-    "ups.efficiency": ["Efficiency", "%", "mdi:gauge"],
+    "ups.efficiency": ["Efficiency", UNIT_PERCENTAGE, "mdi:gauge"],
     "ups.power": ["Current Apparent Power", "VA", "mdi:flash"],
     "ups.power.nominal": ["Nominal Power", "VA", "mdi:flash"],
     "ups.realpower": ["Current Real Power", POWER_WATT, "mdi:flash"],
@@ -77,10 +78,18 @@ SENSOR_TYPES = {
     "ups.start.battery": ["Start on Battery", "", "mdi:information-outline"],
     "ups.start.reboot": ["Reboot on Battery", "", "mdi:information-outline"],
     "ups.shutdown": ["Shutdown Ability", "", "mdi:information-outline"],
-    "battery.charge": ["Battery Charge", "%", "mdi:gauge"],
-    "battery.charge.low": ["Low Battery Setpoint", "%", "mdi:gauge"],
-    "battery.charge.restart": ["Minimum Battery to Start", "%", "mdi:gauge"],
-    "battery.charge.warning": ["Warning Battery Setpoint", "%", "mdi:gauge"],
+    "battery.charge": ["Battery Charge", UNIT_PERCENTAGE, "mdi:gauge"],
+    "battery.charge.low": ["Low Battery Setpoint", UNIT_PERCENTAGE, "mdi:gauge"],
+    "battery.charge.restart": [
+        "Minimum Battery to Start",
+        UNIT_PERCENTAGE,
+        "mdi:gauge",
+    ],
+    "battery.charge.warning": [
+        "Warning Battery Setpoint",
+        UNIT_PERCENTAGE,
+        "mdi:gauge",
+    ],
     "battery.charger.status": ["Charging Status", "", "mdi:information-outline"],
     "battery.voltage": ["Battery Voltage", "V", "mdi:flash"],
     "battery.voltage.nominal": ["Nominal Battery Voltage", "V", "mdi:flash"],
diff --git a/homeassistant/components/octoprint/__init__.py b/homeassistant/components/octoprint/__init__.py
index 06a8ae44f1f..dba7e656aff 100644
--- a/homeassistant/components/octoprint/__init__.py
+++ b/homeassistant/components/octoprint/__init__.py
@@ -20,6 +20,7 @@ from homeassistant.const import (
     CONTENT_TYPE_JSON,
     TEMP_CELSIUS,
     TIME_SECONDS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers import discovery
 import homeassistant.helpers.config_validation as cv
@@ -71,7 +72,13 @@ SENSOR_TYPES = {
     # API Endpoint, Group, Key, unit, icon
     "Temperatures": ["printer", "temperature", "*", TEMP_CELSIUS],
     "Current State": ["printer", "state", "text", None, "mdi:printer-3d"],
-    "Job Percentage": ["job", "progress", "completion", "%", "mdi:file-percent"],
+    "Job Percentage": [
+        "job",
+        "progress",
+        "completion",
+        UNIT_PERCENTAGE,
+        "mdi:file-percent",
+    ],
     "Time Remaining": [
         "job",
         "progress",
diff --git a/homeassistant/components/octoprint/sensor.py b/homeassistant/components/octoprint/sensor.py
index 98d878fc2ea..83b247c39cb 100644
--- a/homeassistant/components/octoprint/sensor.py
+++ b/homeassistant/components/octoprint/sensor.py
@@ -3,7 +3,7 @@ import logging
 
 import requests
 
-from homeassistant.const import TEMP_CELSIUS
+from homeassistant.const import TEMP_CELSIUS, UNIT_PERCENTAGE
 from homeassistant.helpers.entity import Entity
 
 from . import DOMAIN as COMPONENT_DOMAIN, SENSOR_TYPES
@@ -111,7 +111,7 @@ class OctoPrintSensor(Entity):
     def state(self):
         """Return the state of the sensor."""
         sensor_unit = self.unit_of_measurement
-        if sensor_unit in (TEMP_CELSIUS, "%"):
+        if sensor_unit in (TEMP_CELSIUS, UNIT_PERCENTAGE):
             # API sometimes returns null and not 0
             if self._state is None:
                 self._state = 0
diff --git a/homeassistant/components/onewire/sensor.py b/homeassistant/components/onewire/sensor.py
index 6a7f282ac87..41f41a6e93d 100644
--- a/homeassistant/components/onewire/sensor.py
+++ b/homeassistant/components/onewire/sensor.py
@@ -8,7 +8,7 @@ from pyownet import protocol
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_HOST, CONF_PORT, TEMP_CELSIUS
+from homeassistant.const import CONF_HOST, CONF_PORT, TEMP_CELSIUS, UNIT_PERCENTAGE
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 
@@ -60,14 +60,14 @@ HOBBYBOARD_EF = {
 SENSOR_TYPES = {
     # SensorType: [ Measured unit, Unit ]
     "temperature": ["temperature", TEMP_CELSIUS],
-    "humidity": ["humidity", "%"],
-    "humidity_raw": ["humidity", "%"],
+    "humidity": ["humidity", UNIT_PERCENTAGE],
+    "humidity_raw": ["humidity", UNIT_PERCENTAGE],
     "pressure": ["pressure", "mb"],
     "illuminance": ["illuminance", "lux"],
-    "wetness_0": ["wetness", "%"],
-    "wetness_1": ["wetness", "%"],
-    "wetness_2": ["wetness", "%"],
-    "wetness_3": ["wetness", "%"],
+    "wetness_0": ["wetness", UNIT_PERCENTAGE],
+    "wetness_1": ["wetness", UNIT_PERCENTAGE],
+    "wetness_2": ["wetness", UNIT_PERCENTAGE],
+    "wetness_3": ["wetness", UNIT_PERCENTAGE],
     "moisture_0": ["moisture", "cb"],
     "moisture_1": ["moisture", "cb"],
     "moisture_2": ["moisture", "cb"],
diff --git a/homeassistant/components/opentherm_gw/const.py b/homeassistant/components/opentherm_gw/const.py
index 580f9f7b1a4..b8d427ba193 100644
--- a/homeassistant/components/opentherm_gw/const.py
+++ b/homeassistant/components/opentherm_gw/const.py
@@ -6,6 +6,7 @@ from homeassistant.const import (
     TEMP_CELSIUS,
     TIME_HOURS,
     TIME_MINUTES,
+    UNIT_PERCENTAGE,
 )
 
 ATTR_GW_ID = "gateway_id"
@@ -38,7 +39,6 @@ SERVICE_SET_SB_TEMP = "set_setback_temperature"
 UNIT_BAR = "bar"
 UNIT_KW = "kW"
 UNIT_L_MIN = f"L/{TIME_MINUTES}"
-UNIT_PERCENT = "%"
 
 BINARY_SENSOR_INFO = {
     # [device_class, friendly_name format]
@@ -121,7 +121,7 @@ SENSOR_INFO = {
     gw_vars.DATA_MASTER_MEMBERID: [None, None, "Thermostat Member ID {}"],
     gw_vars.DATA_SLAVE_MEMBERID: [None, None, "Boiler Member ID {}"],
     gw_vars.DATA_SLAVE_OEM_FAULT: [None, None, "Boiler OEM Fault Code {}"],
-    gw_vars.DATA_COOLING_CONTROL: [None, UNIT_PERCENT, "Cooling Control Signal {}"],
+    gw_vars.DATA_COOLING_CONTROL: [None, UNIT_PERCENTAGE, "Cooling Control Signal {}"],
     gw_vars.DATA_CONTROL_SETPOINT_2: [
         DEVICE_CLASS_TEMPERATURE,
         TEMP_CELSIUS,
@@ -134,13 +134,13 @@ SENSOR_INFO = {
     ],
     gw_vars.DATA_SLAVE_MAX_RELATIVE_MOD: [
         None,
-        UNIT_PERCENT,
+        UNIT_PERCENTAGE,
         "Boiler Maximum Relative Modulation {}",
     ],
     gw_vars.DATA_SLAVE_MAX_CAPACITY: [None, UNIT_KW, "Boiler Maximum Capacity {}"],
     gw_vars.DATA_SLAVE_MIN_MOD_LEVEL: [
         None,
-        UNIT_PERCENT,
+        UNIT_PERCENTAGE,
         "Boiler Minimum Modulation Level {}",
     ],
     gw_vars.DATA_ROOM_SETPOINT: [
@@ -148,7 +148,7 @@ SENSOR_INFO = {
         TEMP_CELSIUS,
         "Room Setpoint {}",
     ],
-    gw_vars.DATA_REL_MOD_LEVEL: [None, UNIT_PERCENT, "Relative Modulation Level {}"],
+    gw_vars.DATA_REL_MOD_LEVEL: [None, UNIT_PERCENTAGE, "Relative Modulation Level {}"],
     gw_vars.DATA_CH_WATER_PRESS: [None, UNIT_BAR, "Central Heating Water Pressure {}"],
     gw_vars.DATA_DHW_FLOW_RATE: [None, UNIT_L_MIN, "Hot Water Flow Rate {}"],
     gw_vars.DATA_ROOM_SETPOINT_2: [
diff --git a/homeassistant/components/openweathermap/sensor.py b/homeassistant/components/openweathermap/sensor.py
index 5908ccfff06..ce32458f640 100644
--- a/homeassistant/components/openweathermap/sensor.py
+++ b/homeassistant/components/openweathermap/sensor.py
@@ -15,6 +15,7 @@ from homeassistant.const import (
     SPEED_METERS_PER_SECOND,
     TEMP_CELSIUS,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -36,9 +37,9 @@ SENSOR_TYPES = {
     "temperature": ["Temperature", None],
     "wind_speed": ["Wind speed", SPEED_METERS_PER_SECOND],
     "wind_bearing": ["Wind bearing", "°"],
-    "humidity": ["Humidity", "%"],
+    "humidity": ["Humidity", UNIT_PERCENTAGE],
     "pressure": ["Pressure", "mbar"],
-    "clouds": ["Cloud coverage", "%"],
+    "clouds": ["Cloud coverage", UNIT_PERCENTAGE],
     "rain": ["Rain", "mm"],
     "snow": ["Snow", "mm"],
     "weather_code": ["Weather code", None],
diff --git a/homeassistant/components/pi_hole/const.py b/homeassistant/components/pi_hole/const.py
index ca4eea32bd6..94f687d9bfa 100644
--- a/homeassistant/components/pi_hole/const.py
+++ b/homeassistant/components/pi_hole/const.py
@@ -1,6 +1,8 @@
 """Constants for the pi_hole integration."""
 from datetime import timedelta
 
+from homeassistant.const import UNIT_PERCENTAGE
+
 DOMAIN = "pi_hole"
 
 CONF_LOCATION = "location"
@@ -26,7 +28,7 @@ SENSOR_DICT = {
     "ads_blocked_today": ["Ads Blocked Today", "ads", "mdi:close-octagon-outline"],
     "ads_percentage_today": [
         "Ads Percentage Blocked Today",
-        "%",
+        UNIT_PERCENTAGE,
         "mdi:close-octagon-outline",
     ],
     "clients_ever_seen": ["Seen Clients", "clients", "mdi:account-outline"],
diff --git a/homeassistant/components/plaato/sensor.py b/homeassistant/components/plaato/sensor.py
index e7c8033f2ac..34a2a1a42b6 100644
--- a/homeassistant/components/plaato/sensor.py
+++ b/homeassistant/components/plaato/sensor.py
@@ -2,6 +2,7 @@
 
 import logging
 
+from homeassistant.const import UNIT_PERCENTAGE
 from homeassistant.helpers.dispatcher import (
     async_dispatcher_connect,
     async_dispatcher_send,
@@ -145,7 +146,7 @@ class PlaatoSensor(Entity):
         if self._type == ATTR_BPM:
             return "bpm"
         if self._type == ATTR_ABV:
-            return "%"
+            return UNIT_PERCENTAGE
 
         return ""
 
diff --git a/homeassistant/components/plant/__init__.py b/homeassistant/components/plant/__init__.py
index 408c7d1bf36..30542db5e23 100644
--- a/homeassistant/components/plant/__init__.py
+++ b/homeassistant/components/plant/__init__.py
@@ -16,6 +16,7 @@ from homeassistant.const import (
     STATE_UNAVAILABLE,
     STATE_UNKNOWN,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import callback
 from homeassistant.exceptions import HomeAssistantError
@@ -131,14 +132,17 @@ class Plant(Entity):
     """
 
     READINGS = {
-        READING_BATTERY: {ATTR_UNIT_OF_MEASUREMENT: "%", "min": CONF_MIN_BATTERY_LEVEL},
+        READING_BATTERY: {
+            ATTR_UNIT_OF_MEASUREMENT: UNIT_PERCENTAGE,
+            "min": CONF_MIN_BATTERY_LEVEL,
+        },
         READING_TEMPERATURE: {
             ATTR_UNIT_OF_MEASUREMENT: TEMP_CELSIUS,
             "min": CONF_MIN_TEMPERATURE,
             "max": CONF_MAX_TEMPERATURE,
         },
         READING_MOISTURE: {
-            ATTR_UNIT_OF_MEASUREMENT: "%",
+            ATTR_UNIT_OF_MEASUREMENT: UNIT_PERCENTAGE,
             "min": CONF_MIN_MOISTURE,
             "max": CONF_MAX_MOISTURE,
         },
diff --git a/homeassistant/components/point/sensor.py b/homeassistant/components/point/sensor.py
index d8ad22bb470..324565aae50 100644
--- a/homeassistant/components/point/sensor.py
+++ b/homeassistant/components/point/sensor.py
@@ -7,6 +7,7 @@ from homeassistant.const import (
     DEVICE_CLASS_PRESSURE,
     DEVICE_CLASS_TEMPERATURE,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.dispatcher import async_dispatcher_connect
 from homeassistant.util.dt import parse_datetime
@@ -21,7 +22,7 @@ DEVICE_CLASS_SOUND = "sound_level"
 SENSOR_TYPES = {
     DEVICE_CLASS_TEMPERATURE: (None, 1, TEMP_CELSIUS),
     DEVICE_CLASS_PRESSURE: (None, 0, "hPa"),
-    DEVICE_CLASS_HUMIDITY: (None, 1, "%"),
+    DEVICE_CLASS_HUMIDITY: (None, 1, UNIT_PERCENTAGE),
     DEVICE_CLASS_SOUND: ("mdi:ear-hearing", 1, "dBa"),
 }
 
diff --git a/homeassistant/components/prometheus/__init__.py b/homeassistant/components/prometheus/__init__.py
index d77cb4f56da..314695458b0 100644
--- a/homeassistant/components/prometheus/__init__.py
+++ b/homeassistant/components/prometheus/__init__.py
@@ -17,6 +17,7 @@ from homeassistant.const import (
     EVENT_STATE_CHANGED,
     TEMP_CELSIUS,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers import entityfilter, state as state_helper
 import homeassistant.helpers.config_validation as cv
@@ -349,7 +350,7 @@ class PrometheusMetrics:
         units = {
             TEMP_CELSIUS: "c",
             TEMP_FAHRENHEIT: "c",  # F should go into C metric
-            "%": "percent",
+            UNIT_PERCENTAGE: "percent",
         }
         default = unit.replace("/", "_per_")
         default = default.lower()
diff --git a/homeassistant/components/qnap/sensor.py b/homeassistant/components/qnap/sensor.py
index 1ad53f4db48..475e02aba86 100644
--- a/homeassistant/components/qnap/sensor.py
+++ b/homeassistant/components/qnap/sensor.py
@@ -19,6 +19,7 @@ from homeassistant.const import (
     DATA_GIBIBYTES,
     DATA_RATE_MEBIBYTES_PER_SECOND,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.exceptions import PlatformNotReady
 import homeassistant.helpers.config_validation as cv
@@ -61,12 +62,12 @@ _SYSTEM_MON_COND = {
 }
 _CPU_MON_COND = {
     "cpu_temp": ["CPU Temperature", TEMP_CELSIUS, "mdi:thermometer"],
-    "cpu_usage": ["CPU Usage", "%", "mdi:chip"],
+    "cpu_usage": ["CPU Usage", UNIT_PERCENTAGE, "mdi:chip"],
 }
 _MEMORY_MON_COND = {
     "memory_free": ["Memory Available", DATA_GIBIBYTES, "mdi:memory"],
     "memory_used": ["Memory Used", DATA_GIBIBYTES, "mdi:memory"],
-    "memory_percent_used": ["Memory Usage", "%", "mdi:memory"],
+    "memory_percent_used": ["Memory Usage", UNIT_PERCENTAGE, "mdi:memory"],
 }
 _NETWORK_MON_COND = {
     "network_link_status": ["Network Link", None, "mdi:checkbox-marked-circle-outline"],
@@ -80,7 +81,7 @@ _DRIVE_MON_COND = {
 _VOLUME_MON_COND = {
     "volume_size_used": ["Used Space", DATA_GIBIBYTES, "mdi:chart-pie"],
     "volume_size_free": ["Free Space", DATA_GIBIBYTES, "mdi:chart-pie"],
-    "volume_percentage_used": ["Volume Used", "%", "mdi:chart-pie"],
+    "volume_percentage_used": ["Volume Used", UNIT_PERCENTAGE, "mdi:chart-pie"],
 }
 
 _MONITORED_CONDITIONS = (
diff --git a/homeassistant/components/raincloud/__init__.py b/homeassistant/components/raincloud/__init__.py
index 41fefbe8fca..4f9ae7fb733 100644
--- a/homeassistant/components/raincloud/__init__.py
+++ b/homeassistant/components/raincloud/__init__.py
@@ -13,6 +13,7 @@ from homeassistant.const import (
     CONF_USERNAME,
     TIME_DAYS,
     TIME_MINUTES,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.dispatcher import async_dispatcher_connect, dispatcher_send
@@ -58,7 +59,7 @@ ICON_MAP = {
 
 UNIT_OF_MEASUREMENT_MAP = {
     "auto_watering": "",
-    "battery": "%",
+    "battery": UNIT_PERCENTAGE,
     "is_watering": "",
     "manual_watering": "",
     "next_cycle": "",
diff --git a/homeassistant/components/repetier/__init__.py b/homeassistant/components/repetier/__init__.py
index 1d6026a8754..a5a9224464d 100644
--- a/homeassistant/components/repetier/__init__.py
+++ b/homeassistant/components/repetier/__init__.py
@@ -13,6 +13,7 @@ from homeassistant.const import (
     CONF_PORT,
     CONF_SENSORS,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.discovery import load_platform
@@ -123,7 +124,7 @@ SENSOR_TYPES = {
         "_chamber_",
     ],
     "current_state": ["state", None, "mdi:printer-3d", ""],
-    "current_job": ["progress", "%", "mdi:file-percent", "_current_job"],
+    "current_job": ["progress", UNIT_PERCENTAGE, "mdi:file-percent", "_current_job"],
     "job_end": ["progress", None, "mdi:clock-end", "_job_end"],
     "job_start": ["progress", None, "mdi:clock-start", "_job_start"],
 }
diff --git a/homeassistant/components/rfxtrx/__init__.py b/homeassistant/components/rfxtrx/__init__.py
index ceba82cf544..39cbde08c01 100644
--- a/homeassistant/components/rfxtrx/__init__.py
+++ b/homeassistant/components/rfxtrx/__init__.py
@@ -18,6 +18,7 @@ from homeassistant.const import (
     EVENT_HOMEASSISTANT_STOP,
     POWER_WATT,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -47,7 +48,7 @@ DATA_TYPES = OrderedDict(
     [
         ("Temperature", TEMP_CELSIUS),
         ("Temperature2", TEMP_CELSIUS),
-        ("Humidity", "%"),
+        ("Humidity", UNIT_PERCENTAGE),
         ("Barometer", ""),
         ("Wind direction", ""),
         ("Rain rate", ""),
diff --git a/homeassistant/components/ring/sensor.py b/homeassistant/components/ring/sensor.py
index 329077a18e7..84edaf67c22 100644
--- a/homeassistant/components/ring/sensor.py
+++ b/homeassistant/components/ring/sensor.py
@@ -1,6 +1,7 @@
 """This component provides HA sensor support for Ring Door Bell/Chimes."""
 import logging
 
+from homeassistant.const import UNIT_PERCENTAGE
 from homeassistant.core import callback
 from homeassistant.helpers.entity import Entity
 from homeassistant.helpers.icon import icon_for_battery_level
@@ -203,7 +204,7 @@ SENSOR_TYPES = {
     "battery": [
         "Battery",
         ["doorbots", "authorized_doorbots", "stickup_cams"],
-        "%",
+        UNIT_PERCENTAGE,
         None,
         None,
         "battery",
diff --git a/homeassistant/components/sensehat/sensor.py b/homeassistant/components/sensehat/sensor.py
index 980c23f8555..29aa4af967e 100644
--- a/homeassistant/components/sensehat/sensor.py
+++ b/homeassistant/components/sensehat/sensor.py
@@ -7,7 +7,12 @@ from sense_hat import SenseHat
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_DISPLAY_OPTIONS, CONF_NAME, TEMP_CELSIUS
+from homeassistant.const import (
+    CONF_DISPLAY_OPTIONS,
+    CONF_NAME,
+    TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
+)
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 from homeassistant.util import Throttle
@@ -21,7 +26,7 @@ MIN_TIME_BETWEEN_UPDATES = timedelta(seconds=60)
 
 SENSOR_TYPES = {
     "temperature": ["temperature", TEMP_CELSIUS],
-    "humidity": ["humidity", "%"],
+    "humidity": ["humidity", UNIT_PERCENTAGE],
     "pressure": ["pressure", "mb"],
 }
 
diff --git a/homeassistant/components/sht31/sensor.py b/homeassistant/components/sht31/sensor.py
index 8a520377896..3a66b47688c 100644
--- a/homeassistant/components/sht31/sensor.py
+++ b/homeassistant/components/sht31/sensor.py
@@ -13,6 +13,7 @@ from homeassistant.const import (
     CONF_NAME,
     PRECISION_TENTHS,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -140,7 +141,7 @@ class SHTSensorHumidity(SHTSensor):
     @property
     def unit_of_measurement(self):
         """Return the unit of measurement."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     def update(self):
         """Fetch humidity from the sensor."""
diff --git a/homeassistant/components/skybeacon/sensor.py b/homeassistant/components/skybeacon/sensor.py
index cbf394edf47..9bd02aec7c4 100644
--- a/homeassistant/components/skybeacon/sensor.py
+++ b/homeassistant/components/skybeacon/sensor.py
@@ -15,6 +15,7 @@ from homeassistant.const import (
     EVENT_HOMEASSISTANT_STOP,
     STATE_UNKNOWN,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -82,7 +83,7 @@ class SkybeaconHumid(Entity):
     @property
     def unit_of_measurement(self):
         """Return the unit the value is expressed in."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     @property
     def device_state_attributes(self):
diff --git a/homeassistant/components/smappee/sensor.py b/homeassistant/components/smappee/sensor.py
index 4ff0bb5b853..8f1e034dcac 100644
--- a/homeassistant/components/smappee/sensor.py
+++ b/homeassistant/components/smappee/sensor.py
@@ -2,7 +2,12 @@
 from datetime import timedelta
 import logging
 
-from homeassistant.const import ENERGY_KILO_WATT_HOUR, POWER_WATT, VOLUME_CUBIC_METERS
+from homeassistant.const import (
+    ENERGY_KILO_WATT_HOUR,
+    POWER_WATT,
+    UNIT_PERCENTAGE,
+    VOLUME_CUBIC_METERS,
+)
 from homeassistant.helpers.entity import Entity
 
 from . import DATA_SMAPPEE
@@ -21,7 +26,13 @@ SENSOR_TYPES = {
     ],
     "current": ["Current", "mdi:gauge", "local", "A", "current"],
     "voltage": ["Voltage", "mdi:gauge", "local", "V", "voltage"],
-    "active_cosfi": ["Power Factor", "mdi:gauge", "local", "%", "active_cosfi"],
+    "active_cosfi": [
+        "Power Factor",
+        "mdi:gauge",
+        "local",
+        UNIT_PERCENTAGE,
+        "active_cosfi",
+    ],
     "alwayson_today": [
         "Always On Today",
         "mdi:gauge",
@@ -68,14 +79,14 @@ SENSOR_TYPES = {
         "Water Sensor Humidity",
         "mdi:water-percent",
         "water",
-        "%",
+        UNIT_PERCENTAGE,
         "humidity",
     ],
     "water_sensor_battery": [
         "Water Sensor Battery",
         "mdi:battery",
         "water",
-        "%",
+        UNIT_PERCENTAGE,
         "battery",
     ],
 }
diff --git a/homeassistant/components/smartthings/sensor.py b/homeassistant/components/smartthings/sensor.py
index fb04c01c682..630fbaadd3a 100644
--- a/homeassistant/components/smartthings/sensor.py
+++ b/homeassistant/components/smartthings/sensor.py
@@ -16,6 +16,7 @@ from homeassistant.const import (
     POWER_WATT,
     TEMP_CELSIUS,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 
 from . import SmartThingsEntity
@@ -34,8 +35,10 @@ CAPABILITY_TO_SENSORS = {
         Map(Attribute.air_quality, "Air Quality", "CAQI", None)
     ],
     Capability.alarm: [Map(Attribute.alarm, "Alarm", None, None)],
-    Capability.audio_volume: [Map(Attribute.volume, "Volume", "%", None)],
-    Capability.battery: [Map(Attribute.battery, "Battery", "%", DEVICE_CLASS_BATTERY)],
+    Capability.audio_volume: [Map(Attribute.volume, "Volume", UNIT_PERCENTAGE, None)],
+    Capability.battery: [
+        Map(Attribute.battery, "Battery", UNIT_PERCENTAGE, DEVICE_CLASS_BATTERY)
+    ],
     Capability.body_mass_index_measurement: [
         Map(Attribute.bmi_measurement, "Body Mass Index", "kg/m^2", None)
     ],
@@ -109,7 +112,7 @@ CAPABILITY_TO_SENSORS = {
         Map(Attribute.illuminance, "Illuminance", "lux", DEVICE_CLASS_ILLUMINANCE)
     ],
     Capability.infrared_level: [
-        Map(Attribute.infrared_level, "Infrared Level", "%", None)
+        Map(Attribute.infrared_level, "Infrared Level", UNIT_PERCENTAGE, None)
     ],
     Capability.media_input_source: [
         Map(Attribute.input_source, "Media Input Source", None, None)
@@ -147,7 +150,7 @@ CAPABILITY_TO_SENSORS = {
         Map(
             Attribute.humidity,
             "Relative Humidity Measurement",
-            "%",
+            UNIT_PERCENTAGE,
             DEVICE_CLASS_HUMIDITY,
         )
     ],
diff --git a/homeassistant/components/solarlog/const.py b/homeassistant/components/solarlog/const.py
index 933f8014090..26176e97e46 100644
--- a/homeassistant/components/solarlog/const.py
+++ b/homeassistant/components/solarlog/const.py
@@ -1,7 +1,7 @@
 """Constants for the Solar-Log integration."""
 from datetime import timedelta
 
-from homeassistant.const import ENERGY_KILO_WATT_HOUR, POWER_WATT
+from homeassistant.const import ENERGY_KILO_WATT_HOUR, POWER_WATT, UNIT_PERCENTAGE
 
 DOMAIN = "solarlog"
 
@@ -77,7 +77,7 @@ SENSOR_TYPES = {
         POWER_WATT,
         "mdi:solar-power",
     ],
-    "capacity": ["CAPACITY", "capacity", "%", "mdi:solar-power"],
+    "capacity": ["CAPACITY", "capacity", UNIT_PERCENTAGE, "mdi:solar-power"],
     "efficiency": ["EFFICIENCY", "efficiency", "% W/Wp", "mdi:solar-power"],
     "power_available": [
         "powerAVAILABLE",
diff --git a/homeassistant/components/starline/sensor.py b/homeassistant/components/starline/sensor.py
index 0c6cd8de683..8e17caad86c 100644
--- a/homeassistant/components/starline/sensor.py
+++ b/homeassistant/components/starline/sensor.py
@@ -1,6 +1,6 @@
 """Reads vehicle status from StarLine API."""
 from homeassistant.components.sensor import DEVICE_CLASS_TEMPERATURE
-from homeassistant.const import TEMP_CELSIUS
+from homeassistant.const import TEMP_CELSIUS, UNIT_PERCENTAGE
 from homeassistant.helpers.entity import Entity
 from homeassistant.helpers.icon import icon_for_battery_level, icon_for_signal_level
 
@@ -13,7 +13,7 @@ SENSOR_TYPES = {
     "balance": ["Balance", None, None, "mdi:cash-multiple"],
     "ctemp": ["Interior Temperature", DEVICE_CLASS_TEMPERATURE, TEMP_CELSIUS, None],
     "etemp": ["Engine Temperature", DEVICE_CLASS_TEMPERATURE, TEMP_CELSIUS, None],
-    "gsm_lvl": ["GSM Signal", None, "%", None],
+    "gsm_lvl": ["GSM Signal", None, UNIT_PERCENTAGE, None],
 }
 
 
diff --git a/homeassistant/components/startca/sensor.py b/homeassistant/components/startca/sensor.py
index 82106c2da57..b6d90b99302 100644
--- a/homeassistant/components/startca/sensor.py
+++ b/homeassistant/components/startca/sensor.py
@@ -13,6 +13,7 @@ from homeassistant.const import (
     CONF_MONITORED_VARIABLES,
     CONF_NAME,
     DATA_GIGABYTES,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.aiohttp_client import async_get_clientsession
 import homeassistant.helpers.config_validation as cv
@@ -24,13 +25,11 @@ _LOGGER = logging.getLogger(__name__)
 DEFAULT_NAME = "Start.ca"
 CONF_TOTAL_BANDWIDTH = "total_bandwidth"
 
-PERCENT = "%"
-
 MIN_TIME_BETWEEN_UPDATES = timedelta(hours=1)
 REQUEST_TIMEOUT = 5  # seconds
 
 SENSOR_TYPES = {
-    "usage": ["Usage Ratio", PERCENT, "mdi:percent"],
+    "usage": ["Usage Ratio", UNIT_PERCENTAGE, "mdi:percent"],
     "usage_gb": ["Usage", DATA_GIGABYTES, "mdi:download"],
     "limit": ["Data limit", DATA_GIGABYTES, "mdi:download"],
     "used_download": ["Used Download", DATA_GIGABYTES, "mdi:download"],
diff --git a/homeassistant/components/surepetcare/sensor.py b/homeassistant/components/surepetcare/sensor.py
index 8dc9cf30e3c..9c1416479cb 100644
--- a/homeassistant/components/surepetcare/sensor.py
+++ b/homeassistant/components/surepetcare/sensor.py
@@ -4,7 +4,13 @@ from typing import Any, Dict, Optional
 
 from surepy import SureLockStateID, SureProductID
 
-from homeassistant.const import ATTR_VOLTAGE, CONF_ID, CONF_TYPE, DEVICE_CLASS_BATTERY
+from homeassistant.const import (
+    ATTR_VOLTAGE,
+    CONF_ID,
+    CONF_TYPE,
+    DEVICE_CLASS_BATTERY,
+    UNIT_PERCENTAGE,
+)
 from homeassistant.core import callback
 from homeassistant.helpers.dispatcher import async_dispatcher_connect
 from homeassistant.helpers.entity import Entity
@@ -40,10 +46,7 @@ async def async_setup_platform(hass, config, async_add_entities, discovery_info=
         ]:
             entities.append(SureBattery(entity[CONF_ID], sure_type, spc))
 
-        if sure_type in [
-            SureProductID.CAT_FLAP,
-            SureProductID.PET_FLAP,
-        ]:
+        if sure_type in [SureProductID.CAT_FLAP, SureProductID.PET_FLAP]:
             entities.append(Flap(entity[CONF_ID], sure_type, spc))
 
     async_add_entities(entities, True)
@@ -52,9 +55,7 @@ async def async_setup_platform(hass, config, async_add_entities, discovery_info=
 class SurePetcareSensor(Entity):
     """A binary sensor implementation for Sure Petcare Entities."""
 
-    def __init__(
-        self, _id: int, sure_type: SureProductID, spc: SurePetcareAPI,
-    ):
+    def __init__(self, _id: int, sure_type: SureProductID, spc: SurePetcareAPI):
         """Initialize a Sure Petcare sensor."""
 
         self._id = _id
@@ -128,9 +129,7 @@ class Flap(SurePetcareSensor):
         """Return the state attributes of the device."""
         attributes = None
         if self._state:
-            attributes = {
-                "learn_mode": bool(self._state["learn_mode"]),
-            }
+            attributes = {"learn_mode": bool(self._state["learn_mode"])}
 
         return attributes
 
@@ -182,4 +181,4 @@ class SureBattery(SurePetcareSensor):
     @property
     def unit_of_measurement(self) -> str:
         """Return the unit of measurement."""
-        return "%"
+        return UNIT_PERCENTAGE
diff --git a/homeassistant/components/syncthru/sensor.py b/homeassistant/components/syncthru/sensor.py
index e981154a81a..7cd99bdb261 100644
--- a/homeassistant/components/syncthru/sensor.py
+++ b/homeassistant/components/syncthru/sensor.py
@@ -6,7 +6,7 @@ from pysyncthru import SyncThru
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_HOST, CONF_NAME, CONF_RESOURCE
+from homeassistant.const import CONF_HOST, CONF_NAME, CONF_RESOURCE, UNIT_PERCENTAGE
 from homeassistant.helpers import aiohttp_client
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -174,7 +174,7 @@ class SyncThruTonerSensor(SyncThruSensor):
         super().__init__(syncthru, name)
         self._name = f"{name} Toner {color}"
         self._color = color
-        self._unit_of_measurement = "%"
+        self._unit_of_measurement = UNIT_PERCENTAGE
         self._id_suffix = f"_toner_{color}"
 
     def update(self):
@@ -194,7 +194,7 @@ class SyncThruDrumSensor(SyncThruSensor):
         super().__init__(syncthru, name)
         self._name = f"{name} Drum {color}"
         self._color = color
-        self._unit_of_measurement = "%"
+        self._unit_of_measurement = UNIT_PERCENTAGE
         self._id_suffix = f"_drum_{color}"
 
     def update(self):
diff --git a/homeassistant/components/synologydsm/sensor.py b/homeassistant/components/synologydsm/sensor.py
index d10ecaa15ed..84921b3b8d3 100644
--- a/homeassistant/components/synologydsm/sensor.py
+++ b/homeassistant/components/synologydsm/sensor.py
@@ -21,6 +21,7 @@ from homeassistant.const import (
     DATA_RATE_KILOBYTES_PER_SECOND,
     EVENT_HOMEASSISTANT_START,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -37,14 +38,14 @@ DEFAULT_PORT = 5001
 MIN_TIME_BETWEEN_UPDATES = timedelta(minutes=15)
 
 _UTILISATION_MON_COND = {
-    "cpu_other_load": ["CPU Load (Other)", "%", "mdi:chip"],
-    "cpu_user_load": ["CPU Load (User)", "%", "mdi:chip"],
-    "cpu_system_load": ["CPU Load (System)", "%", "mdi:chip"],
-    "cpu_total_load": ["CPU Load (Total)", "%", "mdi:chip"],
-    "cpu_1min_load": ["CPU Load (1 min)", "%", "mdi:chip"],
-    "cpu_5min_load": ["CPU Load (5 min)", "%", "mdi:chip"],
-    "cpu_15min_load": ["CPU Load (15 min)", "%", "mdi:chip"],
-    "memory_real_usage": ["Memory Usage (Real)", "%", "mdi:memory"],
+    "cpu_other_load": ["CPU Load (Other)", UNIT_PERCENTAGE, "mdi:chip"],
+    "cpu_user_load": ["CPU Load (User)", UNIT_PERCENTAGE, "mdi:chip"],
+    "cpu_system_load": ["CPU Load (System)", UNIT_PERCENTAGE, "mdi:chip"],
+    "cpu_total_load": ["CPU Load (Total)", UNIT_PERCENTAGE, "mdi:chip"],
+    "cpu_1min_load": ["CPU Load (1 min)", UNIT_PERCENTAGE, "mdi:chip"],
+    "cpu_5min_load": ["CPU Load (5 min)", UNIT_PERCENTAGE, "mdi:chip"],
+    "cpu_15min_load": ["CPU Load (15 min)", UNIT_PERCENTAGE, "mdi:chip"],
+    "memory_real_usage": ["Memory Usage (Real)", UNIT_PERCENTAGE, "mdi:memory"],
     "memory_size": ["Memory Size", DATA_MEGABYTES, "mdi:memory"],
     "memory_cached": ["Memory Cached", DATA_MEGABYTES, "mdi:memory"],
     "memory_available_swap": ["Memory Available (Swap)", DATA_MEGABYTES, "mdi:memory"],
@@ -59,7 +60,7 @@ _STORAGE_VOL_MON_COND = {
     "volume_device_type": ["Type", None, "mdi:harddisk"],
     "volume_size_total": ["Total Size", None, "mdi:chart-pie"],
     "volume_size_used": ["Used Space", None, "mdi:chart-pie"],
-    "volume_percentage_used": ["Volume Used", "%", "mdi:chart-pie"],
+    "volume_percentage_used": ["Volume Used", UNIT_PERCENTAGE, "mdi:chart-pie"],
     "volume_disk_temp_avg": ["Average Disk Temp", None, "mdi:thermometer"],
     "volume_disk_temp_max": ["Maximum Disk Temp", None, "mdi:thermometer"],
 }
diff --git a/homeassistant/components/systemmonitor/sensor.py b/homeassistant/components/systemmonitor/sensor.py
index 1ea8a409052..bae42c2f50b 100644
--- a/homeassistant/components/systemmonitor/sensor.py
+++ b/homeassistant/components/systemmonitor/sensor.py
@@ -15,6 +15,7 @@ from homeassistant.const import (
     DATA_RATE_MEGABYTES_PER_SECOND,
     STATE_OFF,
     STATE_ON,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -29,7 +30,7 @@ CONF_ARG = "arg"
 SENSOR_TYPES = {
     "disk_free": ["Disk free", DATA_GIBIBYTES, "mdi:harddisk", None],
     "disk_use": ["Disk use", DATA_GIBIBYTES, "mdi:harddisk", None],
-    "disk_use_percent": ["Disk use (percent)", "%", "mdi:harddisk", None],
+    "disk_use_percent": ["Disk use (percent)", UNIT_PERCENTAGE, "mdi:harddisk", None],
     "ipv4_address": ["IPv4 address", "", "mdi:server-network", None],
     "ipv6_address": ["IPv6 address", "", "mdi:server-network", None],
     "last_boot": ["Last boot", "", "mdi:clock", "timestamp"],
@@ -38,7 +39,7 @@ SENSOR_TYPES = {
     "load_5m": ["Load (5m)", " ", "mdi:memory", None],
     "memory_free": ["Memory free", DATA_MEBIBYTES, "mdi:memory", None],
     "memory_use": ["Memory use", DATA_MEBIBYTES, "mdi:memory", None],
-    "memory_use_percent": ["Memory use (percent)", "%", "mdi:memory", None],
+    "memory_use_percent": ["Memory use (percent)", UNIT_PERCENTAGE, "mdi:memory", None],
     "network_in": ["Network in", DATA_MEBIBYTES, "mdi:server-network", None],
     "network_out": ["Network out", DATA_MEBIBYTES, "mdi:server-network", None],
     "packets_in": ["Packets in", " ", "mdi:server-network", None],
@@ -56,10 +57,10 @@ SENSOR_TYPES = {
         None,
     ],
     "process": ["Process", " ", "mdi:memory", None],
-    "processor_use": ["Processor use", "%", "mdi:memory", None],
+    "processor_use": ["Processor use", UNIT_PERCENTAGE, "mdi:memory", None],
     "swap_free": ["Swap free", DATA_MEBIBYTES, "mdi:harddisk", None],
     "swap_use": ["Swap use", DATA_MEBIBYTES, "mdi:harddisk", None],
-    "swap_use_percent": ["Swap use (percent)", "%", "mdi:harddisk", None],
+    "swap_use_percent": ["Swap use (percent)", UNIT_PERCENTAGE, "mdi:harddisk", None],
 }
 
 PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend(
diff --git a/homeassistant/components/tado/sensor.py b/homeassistant/components/tado/sensor.py
index f5f32a6ed1a..2cd40bee3fa 100644
--- a/homeassistant/components/tado/sensor.py
+++ b/homeassistant/components/tado/sensor.py
@@ -1,7 +1,7 @@
 """Support for Tado sensors for each zone."""
 import logging
 
-from homeassistant.const import TEMP_CELSIUS
+from homeassistant.const import TEMP_CELSIUS, UNIT_PERCENTAGE
 from homeassistant.core import callback
 from homeassistant.helpers.dispatcher import async_dispatcher_connect
 from homeassistant.helpers.entity import Entity
@@ -134,9 +134,9 @@ class TadoSensor(Entity):
         if self.zone_variable == "temperature":
             return self.hass.config.units.temperature_unit
         if self.zone_variable == "humidity":
-            return "%"
+            return UNIT_PERCENTAGE
         if self.zone_variable == "heating":
-            return "%"
+            return UNIT_PERCENTAGE
         if self.zone_variable == "ac":
             return ""
 
diff --git a/homeassistant/components/tahoma/sensor.py b/homeassistant/components/tahoma/sensor.py
index fb8c61607c7..20364a243b3 100644
--- a/homeassistant/components/tahoma/sensor.py
+++ b/homeassistant/components/tahoma/sensor.py
@@ -2,7 +2,7 @@
 from datetime import timedelta
 import logging
 
-from homeassistant.const import ATTR_BATTERY_LEVEL, TEMP_CELSIUS
+from homeassistant.const import ATTR_BATTERY_LEVEL, TEMP_CELSIUS, UNIT_PERCENTAGE
 from homeassistant.helpers.entity import Entity
 
 from . import DOMAIN as TAHOMA_DOMAIN, TahomaDevice
@@ -51,7 +51,7 @@ class TahomaSensor(TahomaDevice, Entity):
         if self.tahoma_device.type == "io:LightIOSystemSensor":
             return "lx"
         if self.tahoma_device.type == "Humidity Sensor":
-            return "%"
+            return UNIT_PERCENTAGE
         if self.tahoma_device.type == "rtds:RTDSContactSensor":
             return None
         if self.tahoma_device.type == "rtds:RTDSMotionSensor":
diff --git a/homeassistant/components/tank_utility/sensor.py b/homeassistant/components/tank_utility/sensor.py
index 61a3d7367bf..5847eecc8a8 100644
--- a/homeassistant/components/tank_utility/sensor.py
+++ b/homeassistant/components/tank_utility/sensor.py
@@ -8,7 +8,7 @@ from tank_utility import auth, device as tank_monitor
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_DEVICES, CONF_EMAIL, CONF_PASSWORD
+from homeassistant.const import CONF_DEVICES, CONF_EMAIL, CONF_PASSWORD, UNIT_PERCENTAGE
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 
@@ -26,7 +26,6 @@ PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend(
 
 SENSOR_TYPE = "tank"
 SENSOR_ROUNDING_PRECISION = 1
-SENSOR_UNIT_OF_MEASUREMENT = "%"
 SENSOR_ATTRS = [
     "name",
     "address",
@@ -74,7 +73,7 @@ class TankUtilitySensor(Entity):
         self._device = device
         self._state = None
         self._name = f"Tank Utility {self.device}"
-        self._unit_of_measurement = SENSOR_UNIT_OF_MEASUREMENT
+        self._unit_of_measurement = UNIT_PERCENTAGE
         self._attributes = {}
 
     @property
diff --git a/homeassistant/components/teksavvy/sensor.py b/homeassistant/components/teksavvy/sensor.py
index f340f4a3971..0d2d290fed9 100644
--- a/homeassistant/components/teksavvy/sensor.py
+++ b/homeassistant/components/teksavvy/sensor.py
@@ -11,6 +11,7 @@ from homeassistant.const import (
     CONF_MONITORED_VARIABLES,
     CONF_NAME,
     DATA_GIGABYTES,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.aiohttp_client import async_get_clientsession
 import homeassistant.helpers.config_validation as cv
@@ -22,13 +23,11 @@ _LOGGER = logging.getLogger(__name__)
 DEFAULT_NAME = "TekSavvy"
 CONF_TOTAL_BANDWIDTH = "total_bandwidth"
 
-PERCENT = "%"
-
 MIN_TIME_BETWEEN_UPDATES = timedelta(hours=1)
 REQUEST_TIMEOUT = 5  # seconds
 
 SENSOR_TYPES = {
-    "usage": ["Usage Ratio", PERCENT, "mdi:percent"],
+    "usage": ["Usage Ratio", UNIT_PERCENTAGE, "mdi:percent"],
     "usage_gb": ["Usage", DATA_GIGABYTES, "mdi:download"],
     "limit": ["Data limit", DATA_GIGABYTES, "mdi:download"],
     "onpeak_download": ["On Peak Download", DATA_GIGABYTES, "mdi:download"],
diff --git a/homeassistant/components/tellduslive/sensor.py b/homeassistant/components/tellduslive/sensor.py
index 7aafa38c94f..11411e1d6ea 100644
--- a/homeassistant/components/tellduslive/sensor.py
+++ b/homeassistant/components/tellduslive/sensor.py
@@ -10,6 +10,7 @@ from homeassistant.const import (
     SPEED_METERS_PER_SECOND,
     TEMP_CELSIUS,
     TIME_HOURS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.dispatcher import async_dispatcher_connect
 
@@ -37,7 +38,7 @@ SENSOR_TYPES = {
         None,
         DEVICE_CLASS_TEMPERATURE,
     ],
-    SENSOR_TYPE_HUMIDITY: ["Humidity", "%", None, DEVICE_CLASS_HUMIDITY],
+    SENSOR_TYPE_HUMIDITY: ["Humidity", UNIT_PERCENTAGE, None, DEVICE_CLASS_HUMIDITY],
     SENSOR_TYPE_RAINRATE: ["Rain rate", f"mm/{TIME_HOURS}", "mdi:water", None],
     SENSOR_TYPE_RAINTOTAL: ["Rain total", "mm", "mdi:water", None],
     SENSOR_TYPE_WINDDIRECTION: ["Wind direction", "", "", None],
diff --git a/homeassistant/components/tellstick/sensor.py b/homeassistant/components/tellstick/sensor.py
index 1a55e67ac43..4a3ff75b864 100644
--- a/homeassistant/components/tellstick/sensor.py
+++ b/homeassistant/components/tellstick/sensor.py
@@ -7,7 +7,13 @@ import tellcore.constants as tellcore_constants
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_ID, CONF_NAME, CONF_PROTOCOL, TEMP_CELSIUS
+from homeassistant.const import (
+    CONF_ID,
+    CONF_NAME,
+    CONF_PROTOCOL,
+    TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
+)
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
 
@@ -55,7 +61,9 @@ def setup_platform(hass, config, add_entities, discovery_info=None):
         tellcore_constants.TELLSTICK_TEMPERATURE: DatatypeDescription(
             "temperature", config.get(CONF_TEMPERATURE_SCALE)
         ),
-        tellcore_constants.TELLSTICK_HUMIDITY: DatatypeDescription("humidity", "%"),
+        tellcore_constants.TELLSTICK_HUMIDITY: DatatypeDescription(
+            "humidity", UNIT_PERCENTAGE
+        ),
         tellcore_constants.TELLSTICK_RAINRATE: DatatypeDescription("rain rate", ""),
         tellcore_constants.TELLSTICK_RAINTOTAL: DatatypeDescription("rain total", ""),
         tellcore_constants.TELLSTICK_WINDDIRECTION: DatatypeDescription(
diff --git a/homeassistant/components/thinkingcleaner/sensor.py b/homeassistant/components/thinkingcleaner/sensor.py
index 7a45be7eb61..26175b5368a 100644
--- a/homeassistant/components/thinkingcleaner/sensor.py
+++ b/homeassistant/components/thinkingcleaner/sensor.py
@@ -5,6 +5,7 @@ import logging
 from pythinkingcleaner import Discovery
 
 from homeassistant import util
+from homeassistant.const import UNIT_PERCENTAGE
 from homeassistant.helpers.entity import Entity
 
 _LOGGER = logging.getLogger(__name__)
@@ -13,7 +14,7 @@ MIN_TIME_BETWEEN_SCANS = timedelta(seconds=10)
 MIN_TIME_BETWEEN_FORCED_SCANS = timedelta(milliseconds=100)
 
 SENSOR_TYPES = {
-    "battery": ["Battery", "%", "mdi:battery"],
+    "battery": ["Battery", UNIT_PERCENTAGE, "mdi:battery"],
     "state": ["State", None, None],
     "capacity": ["Capacity", None, None],
 }
diff --git a/homeassistant/components/toon/const.py b/homeassistant/components/toon/const.py
index a22835ec215..239359c1fdf 100644
--- a/homeassistant/components/toon/const.py
+++ b/homeassistant/components/toon/const.py
@@ -18,6 +18,5 @@ DEFAULT_MAX_TEMP = 30.0
 DEFAULT_MIN_TEMP = 6.0
 
 CURRENCY_EUR = "EUR"
-RATIO_PERCENT = "%"
 VOLUME_CM3 = "CM3"
 VOLUME_M3 = "M3"
diff --git a/homeassistant/components/toon/sensor.py b/homeassistant/components/toon/sensor.py
index 79a8fa28540..a5e88bb3d2f 100644
--- a/homeassistant/components/toon/sensor.py
+++ b/homeassistant/components/toon/sensor.py
@@ -2,7 +2,7 @@
 import logging
 
 from homeassistant.config_entries import ConfigEntry
-from homeassistant.const import ENERGY_KILO_WATT_HOUR, POWER_WATT
+from homeassistant.const import ENERGY_KILO_WATT_HOUR, POWER_WATT, UNIT_PERCENTAGE
 from homeassistant.helpers.typing import HomeAssistantType
 
 from . import (
@@ -13,7 +13,7 @@ from . import (
     ToonGasMeterDeviceEntity,
     ToonSolarDeviceEntity,
 )
-from .const import CURRENCY_EUR, DATA_TOON, DOMAIN, RATIO_PERCENT, VOLUME_CM3, VOLUME_M3
+from .const import CURRENCY_EUR, DATA_TOON, DOMAIN, VOLUME_CM3, VOLUME_M3
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -195,7 +195,7 @@ async def async_setup_entry(
                     "current_modulation_level",
                     "Boiler Modulation Level",
                     "mdi:percent",
-                    RATIO_PERCENT,
+                    UNIT_PERCENTAGE,
                 )
             ]
         )
diff --git a/homeassistant/components/tradfri/sensor.py b/homeassistant/components/tradfri/sensor.py
index c3a08ab1675..db12ab0a5cb 100644
--- a/homeassistant/components/tradfri/sensor.py
+++ b/homeassistant/components/tradfri/sensor.py
@@ -1,6 +1,6 @@
 """Support for IKEA Tradfri sensors."""
 
-from homeassistant.const import DEVICE_CLASS_BATTERY
+from homeassistant.const import DEVICE_CLASS_BATTERY, UNIT_PERCENTAGE
 
 from .base_class import TradfriBaseDevice
 from .const import CONF_GATEWAY_ID, KEY_API, KEY_GATEWAY
@@ -47,4 +47,4 @@ class TradfriSensor(TradfriBaseDevice):
     @property
     def unit_of_measurement(self):
         """Return the unit_of_measurement of the device."""
-        return "%"
+        return UNIT_PERCENTAGE
diff --git a/homeassistant/components/trafikverket_weatherstation/sensor.py b/homeassistant/components/trafikverket_weatherstation/sensor.py
index 78f5bbbb8ca..f2e7387aa6b 100644
--- a/homeassistant/components/trafikverket_weatherstation/sensor.py
+++ b/homeassistant/components/trafikverket_weatherstation/sensor.py
@@ -18,6 +18,7 @@ from homeassistant.const import (
     DEVICE_CLASS_TEMPERATURE,
     SPEED_METERS_PER_SECOND,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.aiohttp_client import async_get_clientsession
 import homeassistant.helpers.config_validation as cv
@@ -81,7 +82,7 @@ SENSOR_TYPES = {
     ],
     "humidity": [
         "Humidity",
-        "%",
+        UNIT_PERCENTAGE,
         "humidity",
         "mdi:water-percent",
         DEVICE_CLASS_HUMIDITY,
diff --git a/homeassistant/components/vallox/sensor.py b/homeassistant/components/vallox/sensor.py
index f7be502cecb..5bf9b8061ad 100644
--- a/homeassistant/components/vallox/sensor.py
+++ b/homeassistant/components/vallox/sensor.py
@@ -8,6 +8,7 @@ from homeassistant.const import (
     DEVICE_CLASS_TEMPERATURE,
     DEVICE_CLASS_TIMESTAMP,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import callback
 from homeassistant.helpers.dispatcher import async_dispatcher_connect
@@ -39,7 +40,7 @@ async def async_setup_platform(hass, config, async_add_entities, discovery_info=
             state_proxy=state_proxy,
             metric_key="A_CYC_FAN_SPEED",
             device_class=None,
-            unit_of_measurement="%",
+            unit_of_measurement=UNIT_PERCENTAGE,
             icon="mdi:fan",
         ),
         ValloxSensor(
@@ -79,7 +80,7 @@ async def async_setup_platform(hass, config, async_add_entities, discovery_info=
             state_proxy=state_proxy,
             metric_key="A_CYC_RH_VALUE",
             device_class=DEVICE_CLASS_HUMIDITY,
-            unit_of_measurement="%",
+            unit_of_measurement=UNIT_PERCENTAGE,
             icon=None,
         ),
         ValloxFilterRemainingSensor(
diff --git a/homeassistant/components/vera/sensor.py b/homeassistant/components/vera/sensor.py
index e409a123887..9ac0a36ff9c 100644
--- a/homeassistant/components/vera/sensor.py
+++ b/homeassistant/components/vera/sensor.py
@@ -5,7 +5,7 @@ import logging
 import pyvera as veraApi
 
 from homeassistant.components.sensor import ENTITY_ID_FORMAT
-from homeassistant.const import TEMP_CELSIUS, TEMP_FAHRENHEIT
+from homeassistant.const import TEMP_CELSIUS, TEMP_FAHRENHEIT, UNIT_PERCENTAGE
 from homeassistant.helpers.entity import Entity
 from homeassistant.util import convert
 
@@ -54,7 +54,7 @@ class VeraSensor(VeraDevice, Entity):
         if self.vera_device.category == veraApi.CATEGORY_UV_SENSOR:
             return "level"
         if self.vera_device.category == veraApi.CATEGORY_HUMIDITY_SENSOR:
-            return "%"
+            return UNIT_PERCENTAGE
         if self.vera_device.category == veraApi.CATEGORY_POWER_METER:
             return "watts"
 
diff --git a/homeassistant/components/verisure/sensor.py b/homeassistant/components/verisure/sensor.py
index 5735cea335e..384042b7210 100644
--- a/homeassistant/components/verisure/sensor.py
+++ b/homeassistant/components/verisure/sensor.py
@@ -1,7 +1,7 @@
 """Support for Verisure sensors."""
 import logging
 
-from homeassistant.const import TEMP_CELSIUS
+from homeassistant.const import TEMP_CELSIUS, UNIT_PERCENTAGE
 from homeassistant.helpers.entity import Entity
 
 from . import CONF_HYDROMETERS, CONF_MOUSE, CONF_THERMOMETERS, HUB as hub
@@ -130,7 +130,7 @@ class VerisureHygrometer(Entity):
     @property
     def unit_of_measurement(self):
         """Return the unit of measurement of this entity."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     # pylint: disable=no-self-use
     def update(self):
diff --git a/homeassistant/components/vilfo/const.py b/homeassistant/components/vilfo/const.py
index 1a40b8430d7..0c6414ce99a 100644
--- a/homeassistant/components/vilfo/const.py
+++ b/homeassistant/components/vilfo/const.py
@@ -1,5 +1,5 @@
 """Constants for the Vilfo Router integration."""
-from homeassistant.const import DEVICE_CLASS_TIMESTAMP
+from homeassistant.const import DEVICE_CLASS_TIMESTAMP, UNIT_PERCENTAGE
 
 DOMAIN = "vilfo"
 
@@ -18,12 +18,10 @@ ROUTER_DEFAULT_MODEL = "Vilfo Router"
 ROUTER_DEFAULT_NAME = "Vilfo Router"
 ROUTER_MANUFACTURER = "Vilfo AB"
 
-UNIT_PERCENT = "%"
-
 SENSOR_TYPES = {
     ATTR_LOAD: {
         ATTR_LABEL: "Load",
-        ATTR_UNIT: UNIT_PERCENT,
+        ATTR_UNIT: UNIT_PERCENTAGE,
         ATTR_ICON: "mdi:memory",
         ATTR_API_DATA_FIELD: ATTR_API_DATA_FIELD_LOAD,
     },
diff --git a/homeassistant/components/waterfurnace/sensor.py b/homeassistant/components/waterfurnace/sensor.py
index bf6817c2dfe..e2c92d07f9c 100644
--- a/homeassistant/components/waterfurnace/sensor.py
+++ b/homeassistant/components/waterfurnace/sensor.py
@@ -1,7 +1,7 @@
 """Support for Waterfurnace."""
 
 from homeassistant.components.sensor import ENTITY_ID_FORMAT
-from homeassistant.const import TEMP_FAHRENHEIT
+from homeassistant.const import TEMP_FAHRENHEIT, UNIT_PERCENTAGE
 from homeassistant.core import callback
 from homeassistant.helpers.entity import Entity
 from homeassistant.util import slugify
@@ -34,9 +34,11 @@ SENSORS = [
         "Loop Temp", "enteringwatertemp", "mdi:thermometer", TEMP_FAHRENHEIT
     ),
     WFSensorConfig(
-        "Humidity Set Point", "tstathumidsetpoint", "mdi:water-percent", "%"
+        "Humidity Set Point", "tstathumidsetpoint", "mdi:water-percent", UNIT_PERCENTAGE
+    ),
+    WFSensorConfig(
+        "Humidity", "tstatrelativehumidity", "mdi:water-percent", UNIT_PERCENTAGE
     ),
-    WFSensorConfig("Humidity", "tstatrelativehumidity", "mdi:water-percent", "%"),
     WFSensorConfig("Compressor Power", "compressorpower", "mdi:flash", "W"),
     WFSensorConfig("Fan Power", "fanpower", "mdi:flash", "W"),
     WFSensorConfig("Aux Power", "auxpower", "mdi:flash", "W"),
diff --git a/homeassistant/components/wirelesstag/__init__.py b/homeassistant/components/wirelesstag/__init__.py
index c0a30a8867f..396ca093eec 100644
--- a/homeassistant/components/wirelesstag/__init__.py
+++ b/homeassistant/components/wirelesstag/__init__.py
@@ -11,6 +11,7 @@ from homeassistant.const import (
     ATTR_VOLTAGE,
     CONF_PASSWORD,
     CONF_USERNAME,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.dispatcher import dispatcher_send
@@ -284,5 +285,5 @@ class WirelessTagBaseSensor(Entity):
             ATTR_VOLTAGE: f"{self._tag.battery_volts:.2f}V",
             ATTR_TAG_SIGNAL_STRENGTH: f"{self._tag.signal_strength}dBm",
             ATTR_TAG_OUT_OF_RANGE: not self._tag.is_in_range,
-            ATTR_TAG_POWER_CONSUMPTION: f"{self._tag.power_consumption:.2f}%",
+            ATTR_TAG_POWER_CONSUMPTION: f"{self._tag.power_consumption:.2f}{UNIT_PERCENTAGE}",
         }
diff --git a/homeassistant/components/withings/const.py b/homeassistant/components/withings/const.py
index ea3814d3b3a..781420b347a 100644
--- a/homeassistant/components/withings/const.py
+++ b/homeassistant/components/withings/const.py
@@ -62,6 +62,5 @@ UOM_BEATS_PER_MINUTE = "bpm"
 UOM_BREATHS_PER_MINUTE = f"br/{const.TIME_MINUTES}"
 UOM_FREQUENCY = "times"
 UOM_MMHG = "mmhg"
-UOM_PERCENT = "%"
 UOM_LENGTH_M = const.LENGTH_METERS
 UOM_TEMP_C = const.TEMP_CELSIUS
diff --git a/homeassistant/components/withings/sensor.py b/homeassistant/components/withings/sensor.py
index 0fee2271067..7e58beb4419 100644
--- a/homeassistant/components/withings/sensor.py
+++ b/homeassistant/components/withings/sensor.py
@@ -13,7 +13,12 @@ from withings_api.common import (
 )
 
 from homeassistant.config_entries import ConfigEntry
-from homeassistant.const import MASS_KILOGRAMS, SPEED_METERS_PER_SECOND, TIME_SECONDS
+from homeassistant.const import (
+    MASS_KILOGRAMS,
+    SPEED_METERS_PER_SECOND,
+    TIME_SECONDS,
+    UNIT_PERCENTAGE,
+)
 from homeassistant.core import HomeAssistant
 from homeassistant.helpers import config_entry_oauth2_flow
 from homeassistant.helpers.entity import Entity
@@ -150,7 +155,7 @@ WITHINGS_ATTRIBUTES = [
         const.MEAS_FAT_RATIO_PCT,
         MeasureType.FAT_RATIO,
         "Fat Ratio",
-        const.UOM_PERCENT,
+        UNIT_PERCENTAGE,
         None,
     ),
     WithingsMeasureAttribute(
@@ -175,13 +180,13 @@ WITHINGS_ATTRIBUTES = [
         "mdi:heart-pulse",
     ),
     WithingsMeasureAttribute(
-        const.MEAS_SPO2_PCT, MeasureType.SP02, "SP02", const.UOM_PERCENT, None
+        const.MEAS_SPO2_PCT, MeasureType.SP02, "SP02", UNIT_PERCENTAGE, None
     ),
     WithingsMeasureAttribute(
         const.MEAS_HYDRATION,
         MeasureType.HYDRATION,
         "Hydration",
-        const.UOM_PERCENT,
+        UNIT_PERCENTAGE,
         "mdi:water",
     ),
     WithingsMeasureAttribute(
diff --git a/homeassistant/components/worxlandroid/sensor.py b/homeassistant/components/worxlandroid/sensor.py
index fa2cae53f52..8d651800a77 100644
--- a/homeassistant/components/worxlandroid/sensor.py
+++ b/homeassistant/components/worxlandroid/sensor.py
@@ -7,7 +7,7 @@ import async_timeout
 import voluptuous as vol
 
 from homeassistant.components.sensor import PLATFORM_SCHEMA
-from homeassistant.const import CONF_HOST, CONF_PIN, CONF_TIMEOUT
+from homeassistant.const import CONF_HOST, CONF_PIN, CONF_TIMEOUT, UNIT_PERCENTAGE
 from homeassistant.helpers.aiohttp_client import async_get_clientsession
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -77,7 +77,7 @@ class WorxLandroidSensor(Entity):
     def unit_of_measurement(self):
         """Return the unit of measurement of the sensor."""
         if self.sensor == "battery":
-            return "%"
+            return UNIT_PERCENTAGE
         return None
 
     async def async_update(self):
diff --git a/homeassistant/components/wunderground/sensor.py b/homeassistant/components/wunderground/sensor.py
index 6a1112c028b..de1e48c9c14 100644
--- a/homeassistant/components/wunderground/sensor.py
+++ b/homeassistant/components/wunderground/sensor.py
@@ -26,6 +26,7 @@ from homeassistant.const import (
     SPEED_MILES_PER_HOUR,
     TEMP_CELSIUS,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.exceptions import PlatformNotReady
 from homeassistant.helpers.aiohttp_client import async_get_clientsession
@@ -416,7 +417,7 @@ SENSOR_TYPES = {
         "Relative Humidity",
         "conditions",
         value=lambda wu: int(wu.data["current_observation"]["relative_humidity"][:-1]),
-        unit_of_measurement="%",
+        unit_of_measurement=UNIT_PERCENTAGE,
         icon="mdi:water-percent",
         device_class="humidity",
     ),
@@ -916,16 +917,36 @@ SENSOR_TYPES = {
         "mdi:umbrella",
     ),
     "precip_1d": WUDailySimpleForecastSensorConfig(
-        "Precipitation Probability Today", 0, "pop", None, "%", "mdi:umbrella"
+        "Precipitation Probability Today",
+        0,
+        "pop",
+        None,
+        UNIT_PERCENTAGE,
+        "mdi:umbrella",
     ),
     "precip_2d": WUDailySimpleForecastSensorConfig(
-        "Precipitation Probability Tomorrow", 1, "pop", None, "%", "mdi:umbrella"
+        "Precipitation Probability Tomorrow",
+        1,
+        "pop",
+        None,
+        UNIT_PERCENTAGE,
+        "mdi:umbrella",
     ),
     "precip_3d": WUDailySimpleForecastSensorConfig(
-        "Precipitation Probability in 3 Days", 2, "pop", None, "%", "mdi:umbrella"
+        "Precipitation Probability in 3 Days",
+        2,
+        "pop",
+        None,
+        UNIT_PERCENTAGE,
+        "mdi:umbrella",
     ),
     "precip_4d": WUDailySimpleForecastSensorConfig(
-        "Precipitation Probability in 4 Days", 3, "pop", None, "%", "mdi:umbrella"
+        "Precipitation Probability in 4 Days",
+        3,
+        "pop",
+        None,
+        UNIT_PERCENTAGE,
+        "mdi:umbrella",
     ),
 }
 
diff --git a/homeassistant/components/xiaomi_aqara/sensor.py b/homeassistant/components/xiaomi_aqara/sensor.py
index 5ad29af0aaf..d793f920349 100644
--- a/homeassistant/components/xiaomi_aqara/sensor.py
+++ b/homeassistant/components/xiaomi_aqara/sensor.py
@@ -7,6 +7,7 @@ from homeassistant.const import (
     DEVICE_CLASS_PRESSURE,
     DEVICE_CLASS_TEMPERATURE,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 
 from . import PY_XIAOMI_GATEWAY, XiaomiDevice
@@ -15,7 +16,7 @@ _LOGGER = logging.getLogger(__name__)
 
 SENSOR_TYPES = {
     "temperature": [TEMP_CELSIUS, None, DEVICE_CLASS_TEMPERATURE],
-    "humidity": ["%", None, DEVICE_CLASS_HUMIDITY],
+    "humidity": [UNIT_PERCENTAGE, None, DEVICE_CLASS_HUMIDITY],
     "illumination": ["lm", None, DEVICE_CLASS_ILLUMINANCE],
     "lux": ["lx", None, DEVICE_CLASS_ILLUMINANCE],
     "pressure": ["hPa", None, DEVICE_CLASS_PRESSURE],
diff --git a/homeassistant/components/yr/sensor.py b/homeassistant/components/yr/sensor.py
index 5e7f4ed1db5..c6aaeea7ac9 100644
--- a/homeassistant/components/yr/sensor.py
+++ b/homeassistant/components/yr/sensor.py
@@ -23,6 +23,7 @@ from homeassistant.const import (
     PRESSURE_HPA,
     SPEED_METERS_PER_SECOND,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.aiohttp_client import async_get_clientsession
 import homeassistant.helpers.config_validation as cv
@@ -46,12 +47,12 @@ SENSOR_TYPES = {
     "windGust": ["Wind gust", SPEED_METERS_PER_SECOND, None],
     "pressure": ["Pressure", PRESSURE_HPA, DEVICE_CLASS_PRESSURE],
     "windDirection": ["Wind direction", "°", None],
-    "humidity": ["Humidity", "%", DEVICE_CLASS_HUMIDITY],
-    "fog": ["Fog", "%", None],
-    "cloudiness": ["Cloudiness", "%", None],
-    "lowClouds": ["Low clouds", "%", None],
-    "mediumClouds": ["Medium clouds", "%", None],
-    "highClouds": ["High clouds", "%", None],
+    "humidity": ["Humidity", UNIT_PERCENTAGE, DEVICE_CLASS_HUMIDITY],
+    "fog": ["Fog", UNIT_PERCENTAGE, None],
+    "cloudiness": ["Cloudiness", UNIT_PERCENTAGE, None],
+    "lowClouds": ["Low clouds", UNIT_PERCENTAGE, None],
+    "mediumClouds": ["Medium clouds", UNIT_PERCENTAGE, None],
+    "highClouds": ["High clouds", UNIT_PERCENTAGE, None],
     "dewpointTemperature": [
         "Dewpoint temperature",
         TEMP_CELSIUS,
diff --git a/homeassistant/components/yweather/sensor.py b/homeassistant/components/yweather/sensor.py
index c7f752a8836..db21c430c4d 100644
--- a/homeassistant/components/yweather/sensor.py
+++ b/homeassistant/components/yweather/sensor.py
@@ -16,6 +16,7 @@ from homeassistant.const import (
     CONF_MONITORED_CONDITIONS,
     CONF_NAME,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.entity import Entity
@@ -40,7 +41,7 @@ SENSOR_TYPES = {
     "temp_min": ["Temperature min", "temperature"],
     "temp_max": ["Temperature max", "temperature"],
     "wind_speed": ["Wind speed", "speed"],
-    "humidity": ["Humidity", "%"],
+    "humidity": ["Humidity", UNIT_PERCENTAGE],
     "pressure": ["Pressure", "pressure"],
     "visibility": ["Visibility", "distance"],
 }
diff --git a/homeassistant/components/zamg/sensor.py b/homeassistant/components/zamg/sensor.py
index 74335a2ccdd..a5eb90df218 100644
--- a/homeassistant/components/zamg/sensor.py
+++ b/homeassistant/components/zamg/sensor.py
@@ -18,6 +18,7 @@ from homeassistant.const import (
     CONF_MONITORED_CONDITIONS,
     CONF_NAME,
     SPEED_KILOMETERS_PER_HOUR,
+    UNIT_PERCENTAGE,
     __version__,
 )
 import homeassistant.helpers.config_validation as cv
@@ -39,7 +40,7 @@ MIN_TIME_BETWEEN_UPDATES = timedelta(minutes=10)
 SENSOR_TYPES = {
     "pressure": ("Pressure", "hPa", "LDstat hPa", float),
     "pressure_sealevel": ("Pressure at Sea Level", "hPa", "LDred hPa", float),
-    "humidity": ("Humidity", "%", "RF %", int),
+    "humidity": ("Humidity", UNIT_PERCENTAGE, "RF %", int),
     "wind_speed": (
         "Wind Speed",
         SPEED_KILOMETERS_PER_HOUR,
@@ -54,7 +55,7 @@ SENSOR_TYPES = {
         float,
     ),
     "wind_max_bearing": ("Top Wind Bearing", "°", "WSR °", int),
-    "sun_last_hour": ("Sun Last Hour", "%", "SO %", int),
+    "sun_last_hour": ("Sun Last Hour", UNIT_PERCENTAGE, f"SO {UNIT_PERCENTAGE}", int),
     "temperature": ("Temperature", "°C", "T °C", float),
     "precipitation": ("Precipitation", "l/m²", "N l/m²", float),
     "dewpoint": ("Dew Point", "°C", "TP °C", float),
diff --git a/homeassistant/components/zha/sensor.py b/homeassistant/components/zha/sensor.py
index b98c50d1fa4..e4788acfc53 100644
--- a/homeassistant/components/zha/sensor.py
+++ b/homeassistant/components/zha/sensor.py
@@ -17,6 +17,7 @@ from homeassistant.const import (
     POWER_WATT,
     STATE_UNKNOWN,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import callback
 from homeassistant.helpers.dispatcher import async_dispatcher_connect
@@ -161,7 +162,7 @@ class Battery(Sensor):
     """Battery sensor of power configuration cluster."""
 
     _device_class = DEVICE_CLASS_BATTERY
-    _unit = "%"
+    _unit = UNIT_PERCENTAGE
 
     @staticmethod
     def formatter(value):
@@ -231,7 +232,7 @@ class Humidity(Sensor):
 
     _device_class = DEVICE_CLASS_HUMIDITY
     _divisor = 100
-    _unit = "%"
+    _unit = UNIT_PERCENTAGE
 
 
 @STRICT_MATCH(channel_names=CHANNEL_ILLUMINANCE)
diff --git a/homeassistant/components/zigbee/__init__.py b/homeassistant/components/zigbee/__init__.py
index 3a4fa9029bd..48c96b7591f 100644
--- a/homeassistant/components/zigbee/__init__.py
+++ b/homeassistant/components/zigbee/__init__.py
@@ -15,6 +15,7 @@ from homeassistant.const import (
     CONF_NAME,
     CONF_PIN,
     EVENT_HOMEASSISTANT_STOP,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers import config_validation as cv
 from homeassistant.helpers.dispatcher import async_dispatcher_connect, dispatcher_send
@@ -448,7 +449,7 @@ class ZigBeeAnalogIn(Entity):
     @property
     def unit_of_measurement(self):
         """Return the unit this state is expressed in."""
-        return "%"
+        return UNIT_PERCENTAGE
 
     def update(self):
         """Get the latest reading from the ADC."""
diff --git a/homeassistant/const.py b/homeassistant/const.py
index 155eff79bb3..4e4be408b40 100644
--- a/homeassistant/const.py
+++ b/homeassistant/const.py
@@ -395,6 +395,8 @@ MASS_POUNDS: str = "lb"
 # UV Index units
 UNIT_UV_INDEX: str = "UV index"
 
+# Percentage units
+UNIT_PERCENTAGE = "%"
 # Irradiation units
 IRRADIATION_WATTS_PER_SQUARE_METER = f"{POWER_WATT}/{AREA_SQUARE_METERS}"
 
diff --git a/tests/components/arlo/test_sensor.py b/tests/components/arlo/test_sensor.py
index ac64ad8f272..15b85959ff0 100644
--- a/tests/components/arlo/test_sensor.py
+++ b/tests/components/arlo/test_sensor.py
@@ -9,6 +9,7 @@ from homeassistant.const import (
     ATTR_ATTRIBUTION,
     DEVICE_CLASS_HUMIDITY,
     DEVICE_CLASS_TEMPERATURE,
+    UNIT_PERCENTAGE,
 )
 
 
@@ -168,7 +169,7 @@ def test_sensor_icon(temperature_sensor):
 def test_unit_of_measure(default_sensor, battery_sensor):
     """Test the unit_of_measurement property."""
     assert default_sensor.unit_of_measurement is None
-    assert battery_sensor.unit_of_measurement == "%"
+    assert battery_sensor.unit_of_measurement == UNIT_PERCENTAGE
 
 
 def test_device_class(default_sensor, temperature_sensor, humidity_sensor):
diff --git a/tests/components/awair/test_sensor.py b/tests/components/awair/test_sensor.py
index 03d3f71d5f9..2d88a5019b1 100644
--- a/tests/components/awair/test_sensor.py
+++ b/tests/components/awair/test_sensor.py
@@ -23,6 +23,7 @@ from homeassistant.const import (
     DEVICE_CLASS_TEMPERATURE,
     STATE_UNAVAILABLE,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.setup import async_setup_component
 from homeassistant.util.dt import parse_datetime, utcnow
@@ -156,7 +157,7 @@ async def test_awair_score(hass):
     sensor = hass.states.get("sensor.awair_score")
     assert sensor.state == "78"
     assert sensor.attributes["device_class"] == DEVICE_CLASS_SCORE
-    assert sensor.attributes["unit_of_measurement"] == "%"
+    assert sensor.attributes["unit_of_measurement"] == UNIT_PERCENTAGE
 
 
 async def test_awair_temp(hass):
@@ -176,7 +177,7 @@ async def test_awair_humid(hass):
     sensor = hass.states.get("sensor.awair_humidity")
     assert sensor.state == "32.7"
     assert sensor.attributes["device_class"] == DEVICE_CLASS_HUMIDITY
-    assert sensor.attributes["unit_of_measurement"] == "%"
+    assert sensor.attributes["unit_of_measurement"] == UNIT_PERCENTAGE
 
 
 async def test_awair_co2(hass):
diff --git a/tests/components/canary/test_sensor.py b/tests/components/canary/test_sensor.py
index 7d5e829a347..b9d8be50b90 100644
--- a/tests/components/canary/test_sensor.py
+++ b/tests/components/canary/test_sensor.py
@@ -12,6 +12,7 @@ from homeassistant.components.canary.sensor import (
     STATE_AIR_QUALITY_VERY_ABNORMAL,
     CanarySensor,
 )
+from homeassistant.const import UNIT_PERCENTAGE
 
 from tests.common import get_test_home_assistant
 from tests.components.canary.test_init import mock_device, mock_location
@@ -97,7 +98,7 @@ class TestCanarySensorSetup(unittest.TestCase):
         sensor.update()
 
         assert "Home Family Room Humidity" == sensor.name
-        assert "%" == sensor.unit_of_measurement
+        assert UNIT_PERCENTAGE == sensor.unit_of_measurement
         assert 50.46 == sensor.state
         assert "mdi:water-percent" == sensor.icon
 
@@ -184,7 +185,7 @@ class TestCanarySensorSetup(unittest.TestCase):
         sensor.update()
 
         assert "Home Family Room Battery" == sensor.name
-        assert "%" == sensor.unit_of_measurement
+        assert UNIT_PERCENTAGE == sensor.unit_of_measurement
         assert 70.46 == sensor.state
         assert "mdi:battery-70" == sensor.icon
 
diff --git a/tests/components/dyson/test_sensor.py b/tests/components/dyson/test_sensor.py
index e540d304731..b036e3bbbdb 100644
--- a/tests/components/dyson/test_sensor.py
+++ b/tests/components/dyson/test_sensor.py
@@ -8,7 +8,13 @@ from libpurecool.dyson_pure_cool_link import DysonPureCoolLink
 
 from homeassistant.components import dyson as dyson_parent
 from homeassistant.components.dyson import sensor as dyson
-from homeassistant.const import STATE_OFF, TEMP_CELSIUS, TEMP_FAHRENHEIT, TIME_HOURS
+from homeassistant.const import (
+    STATE_OFF,
+    TEMP_CELSIUS,
+    TEMP_FAHRENHEIT,
+    TIME_HOURS,
+    UNIT_PERCENTAGE,
+)
 from homeassistant.helpers import discovery
 from homeassistant.setup import async_setup_component
 
@@ -169,7 +175,7 @@ class DysonTest(unittest.TestCase):
         sensor.entity_id = "sensor.dyson_1"
         assert not sensor.should_poll
         assert sensor.state is None
-        assert sensor.unit_of_measurement == "%"
+        assert sensor.unit_of_measurement == UNIT_PERCENTAGE
         assert sensor.name == "Device_name Humidity"
         assert sensor.entity_id == "sensor.dyson_1"
 
@@ -180,7 +186,7 @@ class DysonTest(unittest.TestCase):
         sensor.entity_id = "sensor.dyson_1"
         assert not sensor.should_poll
         assert sensor.state == 45
-        assert sensor.unit_of_measurement == "%"
+        assert sensor.unit_of_measurement == UNIT_PERCENTAGE
         assert sensor.name == "Device_name Humidity"
         assert sensor.entity_id == "sensor.dyson_1"
 
@@ -191,7 +197,7 @@ class DysonTest(unittest.TestCase):
         sensor.entity_id = "sensor.dyson_1"
         assert not sensor.should_poll
         assert sensor.state == STATE_OFF
-        assert sensor.unit_of_measurement == "%"
+        assert sensor.unit_of_measurement == UNIT_PERCENTAGE
         assert sensor.name == "Device_name Humidity"
         assert sensor.entity_id == "sensor.dyson_1"
 
diff --git a/tests/components/foobot/test_sensor.py b/tests/components/foobot/test_sensor.py
index a843f9a3012..f8cf38395f2 100644
--- a/tests/components/foobot/test_sensor.py
+++ b/tests/components/foobot/test_sensor.py
@@ -13,6 +13,7 @@ from homeassistant.const import (
     CONCENTRATION_PARTS_PER_BILLION,
     CONCENTRATION_PARTS_PER_MILLION,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.exceptions import PlatformNotReady
 from homeassistant.setup import async_setup_component
@@ -40,10 +41,10 @@ async def test_default_setup(hass, aioclient_mock):
     metrics = {
         "co2": ["1232.0", CONCENTRATION_PARTS_PER_MILLION],
         "temperature": ["21.1", TEMP_CELSIUS],
-        "humidity": ["49.5", "%"],
+        "humidity": ["49.5", UNIT_PERCENTAGE],
         "pm2_5": ["144.8", CONCENTRATION_MICROGRAMS_PER_CUBIC_METER],
         "voc": ["340.7", CONCENTRATION_PARTS_PER_BILLION],
-        "index": ["138.9", "%"],
+        "index": ["138.9", UNIT_PERCENTAGE],
     }
 
     for name, value in metrics.items():
diff --git a/tests/components/homekit/test_get_accessories.py b/tests/components/homekit/test_get_accessories.py
index e6bf185c93b..08a04d5b88e 100644
--- a/tests/components/homekit/test_get_accessories.py
+++ b/tests/components/homekit/test_get_accessories.py
@@ -26,6 +26,7 @@ from homeassistant.const import (
     CONF_TYPE,
     TEMP_CELSIUS,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import State
 
@@ -180,7 +181,7 @@ def test_type_media_player(type_name, entity_id, state, attrs, config):
             "HumiditySensor",
             "sensor.humidity",
             "20",
-            {ATTR_DEVICE_CLASS: "humidity", ATTR_UNIT_OF_MEASUREMENT: "%"},
+            {ATTR_DEVICE_CLASS: "humidity", ATTR_UNIT_OF_MEASUREMENT: UNIT_PERCENTAGE},
         ),
         ("LightSensor", "sensor.light", "900", {ATTR_DEVICE_CLASS: "illuminance"}),
         ("LightSensor", "sensor.light", "900", {ATTR_UNIT_OF_MEASUREMENT: "lm"}),
diff --git a/tests/components/homekit/test_type_lights.py b/tests/components/homekit/test_type_lights.py
index f357702040b..8834f730bce 100644
--- a/tests/components/homekit/test_type_lights.py
+++ b/tests/components/homekit/test_type_lights.py
@@ -21,6 +21,7 @@ from homeassistant.const import (
     STATE_OFF,
     STATE_ON,
     STATE_UNKNOWN,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import CoreState
 from homeassistant.helpers import entity_registry
@@ -127,7 +128,7 @@ async def test_light_brightness(hass, hk_driver, cls, events):
     assert call_turn_on[0].data[ATTR_ENTITY_ID] == entity_id
     assert call_turn_on[0].data[ATTR_BRIGHTNESS_PCT] == 20
     assert len(events) == 1
-    assert events[-1].data[ATTR_VALUE] == "brightness at 20%"
+    assert events[-1].data[ATTR_VALUE] == f"brightness at 20{UNIT_PERCENTAGE}"
 
     await hass.async_add_job(acc.char_on.client_update_value, 1)
     await hass.async_add_job(acc.char_brightness.client_update_value, 40)
@@ -136,7 +137,7 @@ async def test_light_brightness(hass, hk_driver, cls, events):
     assert call_turn_on[1].data[ATTR_ENTITY_ID] == entity_id
     assert call_turn_on[1].data[ATTR_BRIGHTNESS_PCT] == 40
     assert len(events) == 2
-    assert events[-1].data[ATTR_VALUE] == "brightness at 40%"
+    assert events[-1].data[ATTR_VALUE] == f"brightness at 40{UNIT_PERCENTAGE}"
 
     await hass.async_add_job(acc.char_on.client_update_value, 1)
     await hass.async_add_job(acc.char_brightness.client_update_value, 0)
@@ -235,9 +236,7 @@ async def test_light_restore(hass, hk_driver, cls, events):
 
     registry = await entity_registry.async_get_registry(hass)
 
-    registry.async_get_or_create(
-        "light", "hue", "1234", suggested_object_id="simple",
-    )
+    registry.async_get_or_create("light", "hue", "1234", suggested_object_id="simple")
     registry.async_get_or_create(
         "light",
         "hue",
diff --git a/tests/components/homekit/test_type_sensors.py b/tests/components/homekit/test_type_sensors.py
index 969ea0bddc8..79d807b77c5 100644
--- a/tests/components/homekit/test_type_sensors.py
+++ b/tests/components/homekit/test_type_sensors.py
@@ -26,6 +26,7 @@ from homeassistant.const import (
     STATE_UNKNOWN,
     TEMP_CELSIUS,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.core import CoreState
 from homeassistant.helpers import entity_registry
@@ -287,7 +288,7 @@ async def test_sensor_restore(hass, hk_driver, events):
         "12345",
         suggested_object_id="humidity",
         device_class="humidity",
-        unit_of_measurement="%",
+        unit_of_measurement=UNIT_PERCENTAGE,
     )
     hass.bus.async_fire(EVENT_HOMEASSISTANT_START, {})
     await hass.async_block_till_done()
diff --git a/tests/components/homematicip_cloud/test_sensor.py b/tests/components/homematicip_cloud/test_sensor.py
index c5dbef1a499..c55a4682216 100644
--- a/tests/components/homematicip_cloud/test_sensor.py
+++ b/tests/components/homematicip_cloud/test_sensor.py
@@ -27,6 +27,7 @@ from homeassistant.const import (
     POWER_WATT,
     SPEED_KILOMETERS_PER_HOUR,
     TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.setup import async_setup_component
 
@@ -55,7 +56,7 @@ async def test_hmip_accesspoint_status(hass, default_mock_hap_factory):
     )
     assert hmip_device
     assert ha_state.state == "8.0"
-    assert ha_state.attributes[ATTR_UNIT_OF_MEASUREMENT] == "%"
+    assert ha_state.attributes[ATTR_UNIT_OF_MEASUREMENT] == UNIT_PERCENTAGE
 
     await async_manipulate_test_data(hass, hmip_device, "dutyCycle", 17.3)
 
@@ -77,7 +78,7 @@ async def test_hmip_heating_thermostat(hass, default_mock_hap_factory):
     )
 
     assert ha_state.state == "0"
-    assert ha_state.attributes[ATTR_UNIT_OF_MEASUREMENT] == "%"
+    assert ha_state.attributes[ATTR_UNIT_OF_MEASUREMENT] == UNIT_PERCENTAGE
     await async_manipulate_test_data(hass, hmip_device, "valvePosition", 0.37)
     ha_state = hass.states.get(entity_id)
     assert ha_state.state == "37"
@@ -111,7 +112,7 @@ async def test_hmip_humidity_sensor(hass, default_mock_hap_factory):
     )
 
     assert ha_state.state == "40"
-    assert ha_state.attributes["unit_of_measurement"] == "%"
+    assert ha_state.attributes["unit_of_measurement"] == UNIT_PERCENTAGE
     await async_manipulate_test_data(hass, hmip_device, "humidity", 45)
     ha_state = hass.states.get(entity_id)
     assert ha_state.state == "45"
diff --git a/tests/components/influxdb/test_init.py b/tests/components/influxdb/test_init.py
index 1dd2681b7f2..2bb9faad8e5 100644
--- a/tests/components/influxdb/test_init.py
+++ b/tests/components/influxdb/test_init.py
@@ -4,7 +4,13 @@ import unittest
 from unittest import mock
 
 import homeassistant.components.influxdb as influxdb
-from homeassistant.const import EVENT_STATE_CHANGED, STATE_OFF, STATE_ON, STATE_STANDBY
+from homeassistant.const import (
+    EVENT_STATE_CHANGED,
+    STATE_OFF,
+    STATE_ON,
+    STATE_STANDBY,
+    UNIT_PERCENTAGE,
+)
 from homeassistant.setup import setup_component
 
 from tests.common import get_test_home_assistant
@@ -102,7 +108,7 @@ class TestInfluxDB(unittest.TestCase):
                 "unit_of_measurement": "foobars",
                 "longitude": "1.1",
                 "latitude": "2.2",
-                "battery_level": "99%",
+                "battery_level": f"99{UNIT_PERCENTAGE}",
                 "temperature": "20c",
                 "last_seen": "Last seen 23 minutes ago",
                 "updated_at": datetime.datetime(2017, 1, 1, 0, 0),
@@ -124,7 +130,7 @@ class TestInfluxDB(unittest.TestCase):
                     "fields": {
                         "longitude": 1.1,
                         "latitude": 2.2,
-                        "battery_level_str": "99%",
+                        "battery_level_str": f"99{UNIT_PERCENTAGE}",
                         "battery_level": 99.0,
                         "temperature_str": "20c",
                         "temperature": 20.0,
diff --git a/tests/components/min_max/test_sensor.py b/tests/components/min_max/test_sensor.py
index fcc9a72cf7b..38b725226e7 100644
--- a/tests/components/min_max/test_sensor.py
+++ b/tests/components/min_max/test_sensor.py
@@ -7,6 +7,7 @@ from homeassistant.const import (
     STATE_UNKNOWN,
     TEMP_CELSIUS,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.setup import setup_component
 
@@ -233,7 +234,7 @@ class TestMinMaxSensor(unittest.TestCase):
         assert "ERR" == state.attributes.get("unit_of_measurement")
 
         self.hass.states.set(
-            entity_ids[2], self.values[2], {ATTR_UNIT_OF_MEASUREMENT: "%"}
+            entity_ids[2], self.values[2], {ATTR_UNIT_OF_MEASUREMENT: UNIT_PERCENTAGE}
         )
         self.hass.block_till_done()
 
diff --git a/tests/components/mobile_app/test_entity.py b/tests/components/mobile_app/test_entity.py
index 65dc328186d..27ce29ecd15 100644
--- a/tests/components/mobile_app/test_entity.py
+++ b/tests/components/mobile_app/test_entity.py
@@ -2,6 +2,7 @@
 
 import logging
 
+from homeassistant.const import UNIT_PERCENTAGE
 from homeassistant.helpers import device_registry
 
 _LOGGER = logging.getLogger(__name__)
@@ -24,7 +25,7 @@ async def test_sensor(hass, create_registrations, webhook_client):
                 "state": 100,
                 "type": "sensor",
                 "unique_id": "battery_state",
-                "unit_of_measurement": "%",
+                "unit_of_measurement": UNIT_PERCENTAGE,
             },
         },
     )
@@ -40,7 +41,7 @@ async def test_sensor(hass, create_registrations, webhook_client):
 
     assert entity.attributes["device_class"] == "battery"
     assert entity.attributes["icon"] == "mdi:battery"
-    assert entity.attributes["unit_of_measurement"] == "%"
+    assert entity.attributes["unit_of_measurement"] == UNIT_PERCENTAGE
     assert entity.attributes["foo"] == "bar"
     assert entity.domain == "sensor"
     assert entity.name == "Test 1 Battery State"
@@ -104,7 +105,7 @@ async def test_sensor_id_no_dupes(hass, create_registrations, webhook_client):
             "state": 100,
             "type": "sensor",
             "unique_id": "battery_state",
-            "unit_of_measurement": "%",
+            "unit_of_measurement": UNIT_PERCENTAGE,
         },
     }
 
diff --git a/tests/components/mold_indicator/test_sensor.py b/tests/components/mold_indicator/test_sensor.py
index ce0450d3304..bad7430e9b2 100644
--- a/tests/components/mold_indicator/test_sensor.py
+++ b/tests/components/mold_indicator/test_sensor.py
@@ -6,7 +6,12 @@ from homeassistant.components.mold_indicator.sensor import (
     ATTR_DEWPOINT,
 )
 import homeassistant.components.sensor as sensor
-from homeassistant.const import ATTR_UNIT_OF_MEASUREMENT, STATE_UNKNOWN, TEMP_CELSIUS
+from homeassistant.const import (
+    ATTR_UNIT_OF_MEASUREMENT,
+    STATE_UNKNOWN,
+    TEMP_CELSIUS,
+    UNIT_PERCENTAGE,
+)
 from homeassistant.setup import setup_component
 
 from tests.common import get_test_home_assistant
@@ -25,7 +30,7 @@ class TestSensorMoldIndicator(unittest.TestCase):
             "test.outdoortemp", "10", {ATTR_UNIT_OF_MEASUREMENT: TEMP_CELSIUS}
         )
         self.hass.states.set(
-            "test.indoorhumidity", "50", {ATTR_UNIT_OF_MEASUREMENT: "%"}
+            "test.indoorhumidity", "50", {ATTR_UNIT_OF_MEASUREMENT: UNIT_PERCENTAGE}
         )
 
     def tearDown(self):
@@ -50,7 +55,7 @@ class TestSensorMoldIndicator(unittest.TestCase):
 
         moldind = self.hass.states.get("sensor.mold_indicator")
         assert moldind
-        assert "%" == moldind.attributes.get("unit_of_measurement")
+        assert UNIT_PERCENTAGE == moldind.attributes.get("unit_of_measurement")
 
     def test_invalidcalib(self):
         """Test invalid sensor values."""
@@ -61,7 +66,7 @@ class TestSensorMoldIndicator(unittest.TestCase):
             "test.outdoortemp", "10", {ATTR_UNIT_OF_MEASUREMENT: TEMP_CELSIUS}
         )
         self.hass.states.set(
-            "test.indoorhumidity", "0", {ATTR_UNIT_OF_MEASUREMENT: "%"}
+            "test.indoorhumidity", "0", {ATTR_UNIT_OF_MEASUREMENT: UNIT_PERCENTAGE}
         )
 
         assert setup_component(
@@ -94,7 +99,7 @@ class TestSensorMoldIndicator(unittest.TestCase):
             "test.outdoortemp", "10", {ATTR_UNIT_OF_MEASUREMENT: TEMP_CELSIUS}
         )
         self.hass.states.set(
-            "test.indoorhumidity", "-1", {ATTR_UNIT_OF_MEASUREMENT: "%"}
+            "test.indoorhumidity", "-1", {ATTR_UNIT_OF_MEASUREMENT: UNIT_PERCENTAGE}
         )
 
         assert setup_component(
@@ -120,7 +125,7 @@ class TestSensorMoldIndicator(unittest.TestCase):
         assert moldind.attributes.get(ATTR_CRITICAL_TEMP) is None
 
         self.hass.states.set(
-            "test.indoorhumidity", "A", {ATTR_UNIT_OF_MEASUREMENT: "%"}
+            "test.indoorhumidity", "A", {ATTR_UNIT_OF_MEASUREMENT: UNIT_PERCENTAGE}
         )
         self.hass.block_till_done()
         moldind = self.hass.states.get("sensor.mold_indicator")
@@ -220,7 +225,9 @@ class TestSensorMoldIndicator(unittest.TestCase):
             "test.outdoortemp", "25", {ATTR_UNIT_OF_MEASUREMENT: TEMP_CELSIUS}
         )
         self.hass.states.set(
-            "test.indoorhumidity", STATE_UNKNOWN, {ATTR_UNIT_OF_MEASUREMENT: "%"}
+            "test.indoorhumidity",
+            STATE_UNKNOWN,
+            {ATTR_UNIT_OF_MEASUREMENT: UNIT_PERCENTAGE},
         )
         self.hass.block_till_done()
         moldind = self.hass.states.get("sensor.mold_indicator")
@@ -230,7 +237,7 @@ class TestSensorMoldIndicator(unittest.TestCase):
         assert moldind.attributes.get(ATTR_CRITICAL_TEMP) is None
 
         self.hass.states.set(
-            "test.indoorhumidity", "20", {ATTR_UNIT_OF_MEASUREMENT: "%"}
+            "test.indoorhumidity", "20", {ATTR_UNIT_OF_MEASUREMENT: UNIT_PERCENTAGE}
         )
         self.hass.block_till_done()
         moldind = self.hass.states.get("sensor.mold_indicator")
@@ -276,7 +283,7 @@ class TestSensorMoldIndicator(unittest.TestCase):
         assert self.hass.states.get("sensor.mold_indicator").state == "57"
 
         self.hass.states.set(
-            "test.indoorhumidity", "20", {ATTR_UNIT_OF_MEASUREMENT: "%"}
+            "test.indoorhumidity", "20", {ATTR_UNIT_OF_MEASUREMENT: UNIT_PERCENTAGE}
         )
         self.hass.block_till_done()
         assert self.hass.states.get("sensor.mold_indicator").state == "23"
diff --git a/tests/components/rflink/test_sensor.py b/tests/components/rflink/test_sensor.py
index b68e1f959f1..a4904f5bc9b 100644
--- a/tests/components/rflink/test_sensor.py
+++ b/tests/components/rflink/test_sensor.py
@@ -12,7 +12,7 @@ from homeassistant.components.rflink import (
     EVENT_KEY_SENSOR,
     TMP_ENTITY,
 )
-from homeassistant.const import STATE_UNKNOWN
+from homeassistant.const import STATE_UNKNOWN, UNIT_PERCENTAGE
 
 from tests.components.rflink.test_init import mock_rflink
 
@@ -141,7 +141,12 @@ async def test_aliases(hass, monkeypatch):
 
     # test event for config sensor
     event_callback(
-        {"id": "test_alias_02_0", "sensor": "humidity", "value": 65, "unit": "%"}
+        {
+            "id": "test_alias_02_0",
+            "sensor": "humidity",
+            "value": 65,
+            "unit": UNIT_PERCENTAGE,
+        }
     )
     await hass.async_block_till_done()
 
@@ -149,7 +154,7 @@ async def test_aliases(hass, monkeypatch):
     updated_sensor = hass.states.get("sensor.test_02")
     assert updated_sensor
     assert updated_sensor.state == "65"
-    assert updated_sensor.attributes["unit_of_measurement"] == "%"
+    assert updated_sensor.attributes["unit_of_measurement"] == UNIT_PERCENTAGE
 
 
 async def test_race_condition(hass, monkeypatch):
diff --git a/tests/components/rfxtrx/test_sensor.py b/tests/components/rfxtrx/test_sensor.py
index 652c823e0cf..e258ebb9aa1 100644
--- a/tests/components/rfxtrx/test_sensor.py
+++ b/tests/components/rfxtrx/test_sensor.py
@@ -4,7 +4,7 @@ import unittest
 import pytest
 
 from homeassistant.components import rfxtrx as rfxtrx_core
-from homeassistant.const import TEMP_CELSIUS
+from homeassistant.const import TEMP_CELSIUS, UNIT_PERCENTAGE
 from homeassistant.setup import setup_component
 
 from tests.common import get_test_home_assistant, mock_component
@@ -137,7 +137,7 @@ class TestSensorRfxtrx(unittest.TestCase):
                 assert len(rfxtrx_core.RFX_DEVICES[id]) == 2
                 _entity_temp = rfxtrx_core.RFX_DEVICES[id]["Temperature"]
                 _entity_hum = rfxtrx_core.RFX_DEVICES[id]["Humidity"]
-                assert "%" == _entity_hum.unit_of_measurement
+                assert UNIT_PERCENTAGE == _entity_hum.unit_of_measurement
                 assert "Bath" == _entity_hum.__str__()
                 assert _entity_hum.state is None
                 assert TEMP_CELSIUS == _entity_temp.unit_of_measurement
@@ -271,7 +271,7 @@ class TestSensorRfxtrx(unittest.TestCase):
                 assert len(rfxtrx_core.RFX_DEVICES[id]) == 2
                 _entity_temp = rfxtrx_core.RFX_DEVICES[id]["Temperature"]
                 _entity_hum = rfxtrx_core.RFX_DEVICES[id]["Humidity"]
-                assert "%" == _entity_hum.unit_of_measurement
+                assert UNIT_PERCENTAGE == _entity_hum.unit_of_measurement
                 assert "Bath" == _entity_hum.__str__()
                 assert _entity_temp.state is None
                 assert TEMP_CELSIUS == _entity_temp.unit_of_measurement
@@ -303,7 +303,7 @@ class TestSensorRfxtrx(unittest.TestCase):
                 assert len(rfxtrx_core.RFX_DEVICES[id]) == 2
                 _entity_temp = rfxtrx_core.RFX_DEVICES[id]["Temperature"]
                 _entity_hum = rfxtrx_core.RFX_DEVICES[id]["Humidity"]
-                assert "%" == _entity_hum.unit_of_measurement
+                assert UNIT_PERCENTAGE == _entity_hum.unit_of_measurement
                 assert 15 == _entity_hum.state
                 assert {
                     "Battery numeric": 9,
diff --git a/tests/components/sensor/test_device_condition.py b/tests/components/sensor/test_device_condition.py
index f9d8bb640c3..5d25e666110 100644
--- a/tests/components/sensor/test_device_condition.py
+++ b/tests/components/sensor/test_device_condition.py
@@ -4,7 +4,7 @@ import pytest
 import homeassistant.components.automation as automation
 from homeassistant.components.sensor import DOMAIN
 from homeassistant.components.sensor.device_condition import ENTITY_CONDITIONS
-from homeassistant.const import CONF_PLATFORM, STATE_UNKNOWN
+from homeassistant.const import CONF_PLATFORM, STATE_UNKNOWN, UNIT_PERCENTAGE
 from homeassistant.helpers import device_registry
 from homeassistant.setup import async_setup_component
 
@@ -97,13 +97,13 @@ async def test_get_condition_capabilities(hass, device_reg, entity_reg):
     expected_capabilities = {
         "extra_fields": [
             {
-                "description": {"suffix": "%"},
+                "description": {"suffix": UNIT_PERCENTAGE},
                 "name": "above",
                 "optional": True,
                 "type": "float",
             },
             {
-                "description": {"suffix": "%"},
+                "description": {"suffix": UNIT_PERCENTAGE},
                 "name": "below",
                 "optional": True,
                 "type": "float",
diff --git a/tests/components/sensor/test_device_trigger.py b/tests/components/sensor/test_device_trigger.py
index 8e4b5d1792a..54c0c8f7bd0 100644
--- a/tests/components/sensor/test_device_trigger.py
+++ b/tests/components/sensor/test_device_trigger.py
@@ -6,7 +6,7 @@ import pytest
 import homeassistant.components.automation as automation
 from homeassistant.components.sensor import DOMAIN
 from homeassistant.components.sensor.device_trigger import ENTITY_TRIGGERS
-from homeassistant.const import CONF_PLATFORM, STATE_UNKNOWN
+from homeassistant.const import CONF_PLATFORM, STATE_UNKNOWN, UNIT_PERCENTAGE
 from homeassistant.helpers import device_registry
 from homeassistant.setup import async_setup_component
 import homeassistant.util.dt as dt_util
@@ -102,13 +102,13 @@ async def test_get_trigger_capabilities(hass, device_reg, entity_reg):
     expected_capabilities = {
         "extra_fields": [
             {
-                "description": {"suffix": "%"},
+                "description": {"suffix": UNIT_PERCENTAGE},
                 "name": "above",
                 "optional": True,
                 "type": "float",
             },
             {
-                "description": {"suffix": "%"},
+                "description": {"suffix": UNIT_PERCENTAGE},
                 "name": "below",
                 "optional": True,
                 "type": "float",
diff --git a/tests/components/smartthings/test_sensor.py b/tests/components/smartthings/test_sensor.py
index f285bc65d8d..fd8bfdca44c 100644
--- a/tests/components/smartthings/test_sensor.py
+++ b/tests/components/smartthings/test_sensor.py
@@ -13,6 +13,7 @@ from homeassistant.const import (
     ATTR_FRIENDLY_NAME,
     ATTR_UNIT_OF_MEASUREMENT,
     STATE_UNKNOWN,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers.dispatcher import async_dispatcher_send
 
@@ -37,7 +38,7 @@ async def test_entity_state(hass, device_factory):
     await setup_platform(hass, SENSOR_DOMAIN, devices=[device])
     state = hass.states.get("sensor.sensor_1_battery")
     assert state.state == "100"
-    assert state.attributes[ATTR_UNIT_OF_MEASUREMENT] == "%"
+    assert state.attributes[ATTR_UNIT_OF_MEASUREMENT] == UNIT_PERCENTAGE
     assert state.attributes[ATTR_FRIENDLY_NAME] == device.label + " Battery"
 
 
diff --git a/tests/components/sonarr/test_sensor.py b/tests/components/sonarr/test_sensor.py
index 300d201079b..1629a3d29c2 100644
--- a/tests/components/sonarr/test_sensor.py
+++ b/tests/components/sonarr/test_sensor.py
@@ -6,7 +6,7 @@ import unittest
 import pytest
 
 import homeassistant.components.sonarr.sensor as sonarr
-from homeassistant.const import DATA_GIGABYTES
+from homeassistant.const import DATA_GIGABYTES, UNIT_PERCENTAGE
 
 from tests.common import get_test_home_assistant
 
@@ -569,7 +569,10 @@ class TestSonarrSetup(unittest.TestCase):
             assert "mdi:download" == device.icon
             assert "Episodes" == device.unit_of_measurement
             assert "Sonarr Queue" == device.name
-            assert "100.00%" == device.device_state_attributes["Game of Thrones S03E08"]
+            assert (
+                f"100.00{UNIT_PERCENTAGE}"
+                == device.device_state_attributes["Game of Thrones S03E08"]
+            )
 
     @unittest.mock.patch("requests.get", side_effect=mocked_requests_get)
     def test_series(self, req_mock):
diff --git a/tests/components/spaceapi/test_init.py b/tests/components/spaceapi/test_init.py
index 840931d073b..78c7991d9b3 100644
--- a/tests/components/spaceapi/test_init.py
+++ b/tests/components/spaceapi/test_init.py
@@ -5,6 +5,7 @@ from unittest.mock import patch
 import pytest
 
 from homeassistant.components.spaceapi import DOMAIN, SPACEAPI_VERSION, URL_API_SPACEAPI
+from homeassistant.const import UNIT_PERCENTAGE
 from homeassistant.setup import async_setup_component
 
 from tests.common import mock_coro
@@ -62,7 +63,9 @@ SENSOR_OUTPUT = {
         {"location": "Home", "name": "temp1", "unit": "°C", "value": "25"},
         {"location": "Home", "name": "temp2", "unit": "°C", "value": "23"},
     ],
-    "humidity": [{"location": "Home", "name": "hum1", "unit": "%", "value": "88"}],
+    "humidity": [
+        {"location": "Home", "name": "hum1", "unit": UNIT_PERCENTAGE, "value": "88"}
+    ],
 }
 
 
@@ -74,7 +77,9 @@ def mock_client(hass, hass_client):
 
     hass.states.async_set("test.temp1", 25, attributes={"unit_of_measurement": "°C"})
     hass.states.async_set("test.temp2", 23, attributes={"unit_of_measurement": "°C"})
-    hass.states.async_set("test.hum1", 88, attributes={"unit_of_measurement": "%"})
+    hass.states.async_set(
+        "test.hum1", 88, attributes={"unit_of_measurement": UNIT_PERCENTAGE}
+    )
 
     return hass.loop.run_until_complete(hass_client())
 
diff --git a/tests/components/startca/test_sensor.py b/tests/components/startca/test_sensor.py
index 82748c122ab..23cc892900b 100644
--- a/tests/components/startca/test_sensor.py
+++ b/tests/components/startca/test_sensor.py
@@ -1,7 +1,7 @@
 """Tests for the Start.ca sensor platform."""
 from homeassistant.bootstrap import async_setup_component
 from homeassistant.components.startca.sensor import StartcaData
-from homeassistant.const import DATA_GIGABYTES
+from homeassistant.const import DATA_GIGABYTES, UNIT_PERCENTAGE
 from homeassistant.helpers.aiohttp_client import async_get_clientsession
 
 
@@ -52,7 +52,7 @@ async def test_capped_setup(hass, aioclient_mock):
     await async_setup_component(hass, "sensor", {"sensor": config})
 
     state = hass.states.get("sensor.start_ca_usage_ratio")
-    assert state.attributes.get("unit_of_measurement") == "%"
+    assert state.attributes.get("unit_of_measurement") == UNIT_PERCENTAGE
     assert state.state == "76.24"
 
     state = hass.states.get("sensor.start_ca_usage")
@@ -147,7 +147,7 @@ async def test_unlimited_setup(hass, aioclient_mock):
     await async_setup_component(hass, "sensor", {"sensor": config})
 
     state = hass.states.get("sensor.start_ca_usage_ratio")
-    assert state.attributes.get("unit_of_measurement") == "%"
+    assert state.attributes.get("unit_of_measurement") == UNIT_PERCENTAGE
     assert state.state == "0"
 
     state = hass.states.get("sensor.start_ca_usage")
diff --git a/tests/components/teksavvy/test_sensor.py b/tests/components/teksavvy/test_sensor.py
index 641112e6362..e3e7eae36a8 100644
--- a/tests/components/teksavvy/test_sensor.py
+++ b/tests/components/teksavvy/test_sensor.py
@@ -1,7 +1,7 @@
 """Tests for the TekSavvy sensor platform."""
 from homeassistant.bootstrap import async_setup_component
 from homeassistant.components.teksavvy.sensor import TekSavvyData
-from homeassistant.const import DATA_GIGABYTES
+from homeassistant.const import DATA_GIGABYTES, UNIT_PERCENTAGE
 from homeassistant.helpers.aiohttp_client import async_get_clientsession
 
 
@@ -74,7 +74,7 @@ async def test_capped_setup(hass, aioclient_mock):
     assert state.state == "235.57"
 
     state = hass.states.get("sensor.teksavvy_usage_ratio")
-    assert state.attributes.get("unit_of_measurement") == "%"
+    assert state.attributes.get("unit_of_measurement") == UNIT_PERCENTAGE
     assert state.state == "56.69"
 
     state = hass.states.get("sensor.teksavvy_usage")
@@ -159,7 +159,7 @@ async def test_unlimited_setup(hass, aioclient_mock):
     assert state.state == "226.75"
 
     state = hass.states.get("sensor.teksavvy_usage_ratio")
-    assert state.attributes.get("unit_of_measurement") == "%"
+    assert state.attributes.get("unit_of_measurement") == UNIT_PERCENTAGE
     assert state.state == "0"
 
     state = hass.states.get("sensor.teksavvy_remaining")
diff --git a/tests/components/vera/test_sensor.py b/tests/components/vera/test_sensor.py
index da28fc225e0..9e84815d636 100644
--- a/tests/components/vera/test_sensor.py
+++ b/tests/components/vera/test_sensor.py
@@ -13,6 +13,7 @@ from pyvera import (
     VeraSensor,
 )
 
+from homeassistant.const import UNIT_PERCENTAGE
 from homeassistant.core import HomeAssistant
 
 from .common import ComponentFactory
@@ -64,7 +65,7 @@ async def test_temperature_sensor_f(
         vera_component_factory=vera_component_factory,
         category=CATEGORY_TEMPERATURE_SENSOR,
         class_property="temperature",
-        assert_states=(("33", "1"), ("44", "7"),),
+        assert_states=(("33", "1"), ("44", "7")),
         setup_callback=setup_callback,
     )
 
@@ -78,7 +79,7 @@ async def test_temperature_sensor_c(
         vera_component_factory=vera_component_factory,
         category=CATEGORY_TEMPERATURE_SENSOR,
         class_property="temperature",
-        assert_states=(("33", "33"), ("44", "44"),),
+        assert_states=(("33", "33"), ("44", "44")),
     )
 
 
@@ -91,7 +92,7 @@ async def test_light_sensor(
         vera_component_factory=vera_component_factory,
         category=CATEGORY_LIGHT_SENSOR,
         class_property="light",
-        assert_states=(("12", "12"), ("13", "13"),),
+        assert_states=(("12", "12"), ("13", "13")),
         assert_unit_of_measurement="lx",
     )
 
@@ -105,7 +106,7 @@ async def test_uv_sensor(
         vera_component_factory=vera_component_factory,
         category=CATEGORY_UV_SENSOR,
         class_property="light",
-        assert_states=(("12", "12"), ("13", "13"),),
+        assert_states=(("12", "12"), ("13", "13")),
         assert_unit_of_measurement="level",
     )
 
@@ -119,8 +120,8 @@ async def test_humidity_sensor(
         vera_component_factory=vera_component_factory,
         category=CATEGORY_HUMIDITY_SENSOR,
         class_property="humidity",
-        assert_states=(("12", "12"), ("13", "13"),),
-        assert_unit_of_measurement="%",
+        assert_states=(("12", "12"), ("13", "13")),
+        assert_unit_of_measurement=UNIT_PERCENTAGE,
     )
 
 
@@ -133,7 +134,7 @@ async def test_power_meter_sensor(
         vera_component_factory=vera_component_factory,
         category=CATEGORY_POWER_METER,
         class_property="power",
-        assert_states=(("12", "12"), ("13", "13"),),
+        assert_states=(("12", "12"), ("13", "13")),
         assert_unit_of_measurement="watts",
     )
 
@@ -151,7 +152,7 @@ async def test_trippable_sensor(
         vera_component_factory=vera_component_factory,
         category=999,
         class_property="is_tripped",
-        assert_states=((True, "Tripped"), (False, "Not Tripped"), (True, "Tripped"),),
+        assert_states=((True, "Tripped"), (False, "Not Tripped"), (True, "Tripped")),
         setup_callback=setup_callback,
     )
 
@@ -169,7 +170,7 @@ async def test_unknown_sensor(
         vera_component_factory=vera_component_factory,
         category=999,
         class_property="is_tripped",
-        assert_states=((True, "Unknown"), (False, "Unknown"), (True, "Unknown"),),
+        assert_states=((True, "Unknown"), (False, "Unknown"), (True, "Unknown")),
         setup_callback=setup_callback,
     )
 
@@ -187,7 +188,7 @@ async def test_scene_controller_sensor(
     entity_id = "sensor.dev1_1"
 
     component_data = await vera_component_factory.configure_component(
-        hass=hass, devices=(vera_device,),
+        hass=hass, devices=(vera_device,)
     )
     controller = component_data.controller
     update_callback = controller.register.call_args_list[0][0][1]
diff --git a/tests/components/yr/test_sensor.py b/tests/components/yr/test_sensor.py
index d3e3bd6286f..398acd7d554 100644
--- a/tests/components/yr/test_sensor.py
+++ b/tests/components/yr/test_sensor.py
@@ -3,7 +3,7 @@ from datetime import datetime
 from unittest.mock import patch
 
 from homeassistant.bootstrap import async_setup_component
-from homeassistant.const import SPEED_METERS_PER_SECOND
+from homeassistant.const import SPEED_METERS_PER_SECOND, UNIT_PERCENTAGE
 import homeassistant.util.dt as dt_util
 
 from tests.common import assert_setup_component, load_fixture
@@ -63,11 +63,11 @@ async def test_custom_setup(hass, aioclient_mock):
     assert state.state == "103.6"
 
     state = hass.states.get("sensor.yr_humidity")
-    assert state.attributes.get("unit_of_measurement") == "%"
+    assert state.attributes.get("unit_of_measurement") == UNIT_PERCENTAGE
     assert state.state == "55.5"
 
     state = hass.states.get("sensor.yr_fog")
-    assert state.attributes.get("unit_of_measurement") == "%"
+    assert state.attributes.get("unit_of_measurement") == UNIT_PERCENTAGE
     assert state.state == "0.0"
 
     state = hass.states.get("sensor.yr_wind_speed")
@@ -109,11 +109,11 @@ async def test_forecast_setup(hass, aioclient_mock):
     assert state.state == "148.9"
 
     state = hass.states.get("sensor.yr_humidity")
-    assert state.attributes.get("unit_of_measurement") == "%"
+    assert state.attributes.get("unit_of_measurement") == UNIT_PERCENTAGE
     assert state.state == "77.4"
 
     state = hass.states.get("sensor.yr_fog")
-    assert state.attributes.get("unit_of_measurement") == "%"
+    assert state.attributes.get("unit_of_measurement") == UNIT_PERCENTAGE
     assert state.state == "0.0"
 
     state = hass.states.get("sensor.yr_wind_speed")
diff --git a/tests/components/zha/test_sensor.py b/tests/components/zha/test_sensor.py
index b81e8f02c12..fce882c6949 100644
--- a/tests/components/zha/test_sensor.py
+++ b/tests/components/zha/test_sensor.py
@@ -19,6 +19,7 @@ from homeassistant.const import (
     STATE_UNKNOWN,
     TEMP_CELSIUS,
     TEMP_FAHRENHEIT,
+    UNIT_PERCENTAGE,
 )
 from homeassistant.helpers import restore_state
 from homeassistant.util import dt as dt_util
@@ -35,7 +36,7 @@ from .common import (
 async def async_test_humidity(hass, cluster, entity_id):
     """Test humidity sensor."""
     await send_attribute_report(hass, cluster, 0, 1000)
-    assert_state(hass, entity_id, "10.0", "%")
+    assert_state(hass, entity_id, "10.0", UNIT_PERCENTAGE)
 
 
 async def async_test_temperature(hass, cluster, entity_id):
diff --git a/tests/components/zwave/test_sensor.py b/tests/components/zwave/test_sensor.py
index 74e1ef2cd03..d7503eb10fb 100644
--- a/tests/components/zwave/test_sensor.py
+++ b/tests/components/zwave/test_sensor.py
@@ -151,12 +151,12 @@ def test_alarm_sensor_value_changed(mock_openzwave):
     node = MockNode(
         command_classes=[const.COMMAND_CLASS_ALARM, const.COMMAND_CLASS_SENSOR_ALARM]
     )
-    value = MockValue(data=12.34, node=node, units="%")
+    value = MockValue(data=12.34, node=node, units=homeassistant.const.UNIT_PERCENTAGE)
     values = MockEntityValues(primary=value)
 
     device = sensor.get_device(node=node, values=values, node_config={})
     assert device.state == 12.34
-    assert device.unit_of_measurement == "%"
+    assert device.unit_of_measurement == homeassistant.const.UNIT_PERCENTAGE
     value.data = 45.67
     value_changed(value)
     assert device.state == 45.67
diff --git a/tests/helpers/test_entity_platform.py b/tests/helpers/test_entity_platform.py
index ee43f5d4f1d..d9cbbb31561 100644
--- a/tests/helpers/test_entity_platform.py
+++ b/tests/helpers/test_entity_platform.py
@@ -7,6 +7,7 @@ from unittest.mock import MagicMock, Mock, patch
 import asynctest
 import pytest
 
+from homeassistant.const import UNIT_PERCENTAGE
 from homeassistant.exceptions import PlatformNotReady
 from homeassistant.helpers import entity_platform, entity_registry
 from homeassistant.helpers.entity import async_generate_entity_id
@@ -800,7 +801,7 @@ async def test_entity_info_added_to_entity_registry(hass):
         capability_attributes={"max": 100},
         supported_features=5,
         device_class="mock-device-class",
-        unit_of_measurement="%",
+        unit_of_measurement=UNIT_PERCENTAGE,
     )
 
     await component.async_add_entities([entity_default])
@@ -812,7 +813,7 @@ async def test_entity_info_added_to_entity_registry(hass):
     assert entry_default.capabilities == {"max": 100}
     assert entry_default.supported_features == 5
     assert entry_default.device_class == "mock-device-class"
-    assert entry_default.unit_of_measurement == "%"
+    assert entry_default.unit_of_measurement == UNIT_PERCENTAGE
 
 
 async def test_override_restored_entities(hass):
diff --git a/tests/testing_config/custom_components/test/sensor.py b/tests/testing_config/custom_components/test/sensor.py
index 26497b16a16..38bf9653938 100644
--- a/tests/testing_config/custom_components/test/sensor.py
+++ b/tests/testing_config/custom_components/test/sensor.py
@@ -4,6 +4,7 @@ Provide a mock sensor platform.
 Call init before using it in your tests to ensure clean test data.
 """
 import homeassistant.components.sensor as sensor
+from homeassistant.const import UNIT_PERCENTAGE
 
 from tests.common import MockEntity
 
@@ -11,8 +12,8 @@ DEVICE_CLASSES = list(sensor.DEVICE_CLASSES)
 DEVICE_CLASSES.append("none")
 
 UNITS_OF_MEASUREMENT = {
-    sensor.DEVICE_CLASS_BATTERY: "%",  # % of battery that is left
-    sensor.DEVICE_CLASS_HUMIDITY: "%",  # % of humidity in the air
+    sensor.DEVICE_CLASS_BATTERY: UNIT_PERCENTAGE,  # % of battery that is left
+    sensor.DEVICE_CLASS_HUMIDITY: UNIT_PERCENTAGE,  # % of humidity in the air
     sensor.DEVICE_CLASS_ILLUMINANCE: "lm",  # current light level (lx/lm)
     sensor.DEVICE_CLASS_SIGNAL_STRENGTH: "dB",  # signal strength (dB/dBm)
     sensor.DEVICE_CLASS_TEMPERATURE: "C",  # temperature (C/F)