diff --git a/homeassistant/components/number/const.py b/homeassistant/components/number/const.py
index ec60462351758..402592888a2f6 100644
--- a/homeassistant/components/number/const.py
+++ b/homeassistant/components/number/const.py
@@ -124,7 +124,7 @@ class NumberDeviceClass(StrEnum):
     CO = "carbon_monoxide"
     """Carbon Monoxide gas concentration.
 
-    Unit of measurement: `ppm` (parts per million)
+    Unit of measurement: `ppm` (parts per million), mg/m³
     """
 
     CO2 = "carbon_dioxide"
@@ -469,7 +469,10 @@ class NumberDeviceClass(StrEnum):
     NumberDeviceClass.ATMOSPHERIC_PRESSURE: set(UnitOfPressure),
     NumberDeviceClass.BATTERY: {PERCENTAGE},
     NumberDeviceClass.BLOOD_GLUCOSE_CONCENTRATION: set(UnitOfBloodGlucoseConcentration),
-    NumberDeviceClass.CO: {CONCENTRATION_PARTS_PER_MILLION},
+    NumberDeviceClass.CO: {
+        CONCENTRATION_PARTS_PER_MILLION,
+        CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
+    },
     NumberDeviceClass.CO2: {CONCENTRATION_PARTS_PER_MILLION},
     NumberDeviceClass.CONDUCTIVITY: set(UnitOfConductivity),
     NumberDeviceClass.CURRENT: set(UnitOfElectricCurrent),
diff --git a/homeassistant/components/recorder/statistics.py b/homeassistant/components/recorder/statistics.py
index 2321da45bb9a7..c2a8a6c7607c5 100644
--- a/homeassistant/components/recorder/statistics.py
+++ b/homeassistant/components/recorder/statistics.py
@@ -46,6 +46,7 @@
     AreaConverter,
     BaseUnitConverter,
     BloodGlucoseConcentrationConverter,
+    CarbonMonoxideConcentrationConverter,
     ConductivityConverter,
     DataRateConverter,
     DistanceConverter,
@@ -204,6 +205,10 @@ def query_circular_mean(table: type[StatisticsBase]) -> tuple[Label, Label]:
     **dict.fromkeys(
         MassVolumeConcentrationConverter.VALID_UNITS, MassVolumeConcentrationConverter
     ),
+    **dict.fromkeys(
+        CarbonMonoxideConcentrationConverter.VALID_UNITS,
+        CarbonMonoxideConcentrationConverter,
+    ),
     **dict.fromkeys(ConductivityConverter.VALID_UNITS, ConductivityConverter),
     **dict.fromkeys(DataRateConverter.VALID_UNITS, DataRateConverter),
     **dict.fromkeys(DistanceConverter.VALID_UNITS, DistanceConverter),
diff --git a/homeassistant/components/recorder/websocket_api.py b/homeassistant/components/recorder/websocket_api.py
index 4f798fb86d01e..c65a11cee2ae5 100644
--- a/homeassistant/components/recorder/websocket_api.py
+++ b/homeassistant/components/recorder/websocket_api.py
@@ -19,6 +19,7 @@
     ApparentPowerConverter,
     AreaConverter,
     BloodGlucoseConcentrationConverter,
+    CarbonMonoxideConcentrationConverter,
     ConductivityConverter,
     DataRateConverter,
     DistanceConverter,
@@ -66,6 +67,9 @@
         vol.Optional("blood_glucose_concentration"): vol.In(
             BloodGlucoseConcentrationConverter.VALID_UNITS
         ),
+        vol.Optional("carbon_monoxide"): vol.In(
+            CarbonMonoxideConcentrationConverter.VALID_UNITS
+        ),
         vol.Optional("concentration"): vol.In(
             MassVolumeConcentrationConverter.VALID_UNITS
         ),
diff --git a/homeassistant/components/sensor/const.py b/homeassistant/components/sensor/const.py
index 7d21b68019d03..098ac960fe89e 100644
--- a/homeassistant/components/sensor/const.py
+++ b/homeassistant/components/sensor/const.py
@@ -51,6 +51,7 @@
     AreaConverter,
     BaseUnitConverter,
     BloodGlucoseConcentrationConverter,
+    CarbonMonoxideConcentrationConverter,
     ConductivityConverter,
     DataRateConverter,
     DistanceConverter,
@@ -156,7 +157,7 @@ class SensorDeviceClass(StrEnum):
     CO = "carbon_monoxide"
     """Carbon Monoxide gas concentration.
 
-    Unit of measurement: `ppm` (parts per million)
+    Unit of measurement: `ppm` (parts per million), `mg/m³`
     """
 
     CO2 = "carbon_dioxide"
@@ -537,6 +538,7 @@ class SensorStateClass(StrEnum):
     SensorDeviceClass.AREA: AreaConverter,
     SensorDeviceClass.ATMOSPHERIC_PRESSURE: PressureConverter,
     SensorDeviceClass.BLOOD_GLUCOSE_CONCENTRATION: BloodGlucoseConcentrationConverter,
+    SensorDeviceClass.CO: CarbonMonoxideConcentrationConverter,
     SensorDeviceClass.CONDUCTIVITY: ConductivityConverter,
     SensorDeviceClass.CURRENT: ElectricCurrentConverter,
     SensorDeviceClass.DATA_RATE: DataRateConverter,
@@ -578,7 +580,10 @@ class SensorStateClass(StrEnum):
     SensorDeviceClass.ATMOSPHERIC_PRESSURE: set(UnitOfPressure),
     SensorDeviceClass.BATTERY: {PERCENTAGE},
     SensorDeviceClass.BLOOD_GLUCOSE_CONCENTRATION: set(UnitOfBloodGlucoseConcentration),
-    SensorDeviceClass.CO: {CONCENTRATION_PARTS_PER_MILLION},
+    SensorDeviceClass.CO: {
+        CONCENTRATION_PARTS_PER_MILLION,
+        CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
+    },
     SensorDeviceClass.CO2: {CONCENTRATION_PARTS_PER_MILLION},
     SensorDeviceClass.CONDUCTIVITY: set(UnitOfConductivity),
     SensorDeviceClass.CURRENT: set(UnitOfElectricCurrent),
diff --git a/homeassistant/util/unit_conversion.py b/homeassistant/util/unit_conversion.py
index f969a613a4786..75e515cd95c5d 100644
--- a/homeassistant/util/unit_conversion.py
+++ b/homeassistant/util/unit_conversion.py
@@ -168,6 +168,20 @@ def _are_unit_inverses(cls, from_unit: str | None, to_unit: str | None) -> bool:
         return (from_unit in cls._UNIT_INVERSES) != (to_unit in cls._UNIT_INVERSES)
 
 
+class CarbonMonoxideConcentrationConverter(BaseUnitConverter):
+    """Convert carbon monoxide ratio to mass per volume."""
+
+    UNIT_CLASS = "carbon_monoxide"
+    _UNIT_CONVERSION: dict[str | None, float] = {
+        CONCENTRATION_PARTS_PER_MILLION: 1,
+        CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER: 1.145609,
+    }
+    VALID_UNITS = {
+        CONCENTRATION_PARTS_PER_MILLION,
+        CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
+    }
+
+
 class DataRateConverter(BaseUnitConverter):
     """Utility to convert data rate values."""
 
diff --git a/tests/components/sensor/test_init.py b/tests/components/sensor/test_init.py
index c31abe62826a9..84dcf7742d873 100644
--- a/tests/components/sensor/test_init.py
+++ b/tests/components/sensor/test_init.py
@@ -3007,7 +3007,6 @@ def test_device_class_converters_are_complete() -> None:
     no_converter_device_classes = {
         SensorDeviceClass.AQI,
         SensorDeviceClass.BATTERY,
-        SensorDeviceClass.CO,
         SensorDeviceClass.CO2,
         SensorDeviceClass.DATE,
         SensorDeviceClass.ENUM,
diff --git a/tests/util/test_unit_conversion.py b/tests/util/test_unit_conversion.py
index d9377779b68e8..0d14a30a1b87b 100644
--- a/tests/util/test_unit_conversion.py
+++ b/tests/util/test_unit_conversion.py
@@ -44,6 +44,7 @@
     AreaConverter,
     BaseUnitConverter,
     BloodGlucoseConcentrationConverter,
+    CarbonMonoxideConcentrationConverter,
     ConductivityConverter,
     DataRateConverter,
     DistanceConverter,
@@ -78,6 +79,7 @@
         AreaConverter,
         BloodGlucoseConcentrationConverter,
         MassVolumeConcentrationConverter,
+        CarbonMonoxideConcentrationConverter,
         ConductivityConverter,
         DataRateConverter,
         DistanceConverter,
@@ -114,6 +116,11 @@
         UnitOfBloodGlucoseConcentration.MILLIMOLE_PER_LITER,
         18,
     ),
+    CarbonMonoxideConcentrationConverter: (
+        CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
+        CONCENTRATION_PARTS_PER_MILLION,
+        1.145609,
+    ),
     ConductivityConverter: (
         UnitOfConductivity.MICROSIEMENS_PER_CM,
         UnitOfConductivity.MILLISIEMENS_PER_CM,
@@ -280,6 +287,20 @@
             UnitOfBloodGlucoseConcentration.MILLIGRAMS_PER_DECILITER,
         ),
     ],
+    CarbonMonoxideConcentrationConverter: [
+        (
+            1,
+            CONCENTRATION_PARTS_PER_MILLION,
+            1.145609,
+            CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
+        ),
+        (
+            120,
+            CONCENTRATION_MILLIGRAMS_PER_CUBIC_METER,
+            104.74778,
+            CONCENTRATION_PARTS_PER_MILLION,
+        ),
+    ],
     ConductivityConverter: [
         # Deprecated to deprecated
         (5, UnitOfConductivity.SIEMENS, 5e3, UnitOfConductivity.MILLISIEMENS),