Get suggested_unit_of_measurement via unit converter's UNIT_CLASS (#119196)

Co-authored-by: Richard <rikroe@users.noreply.github.com>
Co-authored-by: Erik Montnemery <erik@montnemery.com>

homeassistant/components/sensor/__init__.py

@@ -394,11 +394,20 @@ class SensorEntity(Entity, cached_properties=CACHED_PROPERTIES_WITH_ATTR_):
         suggested_unit_of_measurement = self.suggested_unit_of_measurement
 
         if suggested_unit_of_measurement is None:
-            # Fallback to suggested by the unit conversion rules
+            # Fallback to unit suggested by the unit conversion rules from device class
             suggested_unit_of_measurement = self.hass.config.units.get_converted_unit(
                 self.device_class, self.native_unit_of_measurement
             )
 
+        if suggested_unit_of_measurement is None and (
+            unit_converter := UNIT_CONVERTERS.get(self.device_class)
+        ):
+            # If the device class is not known by the unit system but has a unit converter,
+            # fall back to the unit suggested by the unit converter's unit class.
+            suggested_unit_of_measurement = self.hass.config.units.get_converted_unit(
+                unit_converter.UNIT_CLASS, self.native_unit_of_measurement
+            )
+
         if suggested_unit_of_measurement is None:
             return UNDEFINED
 

tests/components/sensor/test_init.py

@@ -942,7 +942,21 @@ async def test_custom_unit_change(
             "1000000",
             "1093613",
             SensorDeviceClass.DISTANCE,
-        )
+        ),
+        # Volume Storage (subclass of Volume)
+        (
+            US_CUSTOMARY_SYSTEM,
+            UnitOfVolume.LITERS,
+            UnitOfVolume.GALLONS,
+            UnitOfVolume.GALLONS,
+            UnitOfVolume.FLUID_OUNCES,
+            1000,
+            "1000",
+            "264",
+            "264",
+            "33814",
+            SensorDeviceClass.VOLUME_STORAGE,
+        ),
     ],
 )
 async def test_unit_conversion_priority(