diff --git a/homeassistant/components/number/const.py b/homeassistant/components/number/const.py
index 55b8335acc5..d63f2ff1657 100644
--- a/homeassistant/components/number/const.py
+++ b/homeassistant/components/number/const.py
@@ -432,7 +432,7 @@ class NumberDeviceClass(StrEnum):
 
     Unit of measurement: UnitOfVolumeFlowRate
     - SI / metric: `m³/h`, `m³/min`, `m³/s`, `L/h`, `L/min`, `L/s`, `mL/s`
-    - USCS / imperial: `ft³/min`, `gal/min`
+    - USCS / imperial: `ft³/min`, `gal/min`, `gal/d`
     """
 
     WATER = "water"
diff --git a/homeassistant/components/sensor/const.py b/homeassistant/components/sensor/const.py
index 2731e9f6b03..b9ded0dbe7b 100644
--- a/homeassistant/components/sensor/const.py
+++ b/homeassistant/components/sensor/const.py
@@ -468,7 +468,7 @@ class SensorDeviceClass(StrEnum):
 
     Unit of measurement: UnitOfVolumeFlowRate
     - SI / metric: `m³/h`, `m³/min`, `m³/s`, `L/h`, `L/min`, `L/s`, `mL/s`
-    - USCS / imperial: `ft³/min`, `gal/min`
+    - USCS / imperial: `ft³/min`, `gal/min`, `gal/d`
     """
 
     WATER = "water"
diff --git a/homeassistant/const.py b/homeassistant/const.py
index 01da32e47d9..17426dd6344 100644
--- a/homeassistant/const.py
+++ b/homeassistant/const.py
@@ -653,6 +653,7 @@ class UnitOfVolumeFlowRate(StrEnum):
     LITERS_PER_SECOND = "L/s"
     GALLONS_PER_HOUR = "gal/h"
     GALLONS_PER_MINUTE = "gal/min"
+    GALLONS_PER_DAY = "gal/d"
     MILLILITERS_PER_SECOND = "mL/s"
 
 
diff --git a/homeassistant/util/unit_conversion.py b/homeassistant/util/unit_conversion.py
index b25895c3e8f..d1c77a89170 100644
--- a/homeassistant/util/unit_conversion.py
+++ b/homeassistant/util/unit_conversion.py
@@ -69,7 +69,8 @@ _HECTARE_TO_M2 = 100 * 100  # 1 hectare = 10,000 m²
 _MIN_TO_SEC = 60  # 1 min = 60 seconds
 _HRS_TO_MINUTES = 60  # 1 hr = 60 minutes
 _HRS_TO_SECS = _HRS_TO_MINUTES * _MIN_TO_SEC  # 1 hr = 60 minutes = 3600 seconds
-_DAYS_TO_SECS = 24 * _HRS_TO_SECS  # 1 day = 24 hours = 86400 seconds
+_DAYS_TO_HRS = 24  # 1 day = 24 hours
+_DAYS_TO_SECS = _DAYS_TO_HRS * _HRS_TO_SECS  # 1 day = 24 hours = 86400 seconds
 
 # Energy conversion constants
 _WH_TO_J = 3600  # 1 Wh = 3600 J
@@ -852,6 +853,7 @@ class VolumeFlowRateConverter(BaseUnitConverter):
         UnitOfVolumeFlowRate.GALLONS_PER_HOUR: 1 / _GALLON_TO_CUBIC_METER,
         UnitOfVolumeFlowRate.GALLONS_PER_MINUTE: 1
         / (_HRS_TO_MINUTES * _GALLON_TO_CUBIC_METER),
+        UnitOfVolumeFlowRate.GALLONS_PER_DAY: _DAYS_TO_HRS / _GALLON_TO_CUBIC_METER,
         UnitOfVolumeFlowRate.MILLILITERS_PER_SECOND: 1
         / (_HRS_TO_SECS * _ML_TO_CUBIC_METER),
     }
@@ -865,6 +867,7 @@ class VolumeFlowRateConverter(BaseUnitConverter):
         UnitOfVolumeFlowRate.LITERS_PER_SECOND,
         UnitOfVolumeFlowRate.GALLONS_PER_HOUR,
         UnitOfVolumeFlowRate.GALLONS_PER_MINUTE,
+        UnitOfVolumeFlowRate.GALLONS_PER_DAY,
         UnitOfVolumeFlowRate.MILLILITERS_PER_SECOND,
     }
 
diff --git a/tests/util/test_unit_conversion.py b/tests/util/test_unit_conversion.py
index 345c0bbfd51..8a3ce093935 100644
--- a/tests/util/test_unit_conversion.py
+++ b/tests/util/test_unit_conversion.py
@@ -1054,6 +1054,12 @@ _CONVERTED_VALUE: dict[
             10,
             UnitOfVolumeFlowRate.LITERS_PER_SECOND,
         ),
+        (
+            24,
+            UnitOfVolumeFlowRate.GALLONS_PER_DAY,
+            1,
+            UnitOfVolumeFlowRate.GALLONS_PER_HOUR,
+        ),
     ],
 }