diff --git a/homeassistant/components/mill/sensor.py b/homeassistant/components/mill/sensor.py
index 776ba1dc632..50db999186f 100644
--- a/homeassistant/components/mill/sensor.py
+++ b/homeassistant/components/mill/sensor.py
@@ -86,6 +86,7 @@ SENSOR_TYPES: tuple[SensorEntityDescription, ...] = (
         device_class=SensorDeviceClass.CO2,
         native_unit_of_measurement=CONCENTRATION_PARTS_PER_MILLION,
         name="Estimated CO2",
+        state_class=SensorStateClass.MEASUREMENT,
     ),
     SensorEntityDescription(
         key=TVOC,