The gallon per hour is a unit of volumetric flow rate equal to one imperial gallon passing a point every hour. Its symbol is gal/h, often abbreviated GPH. One imperial gallon is 4.54609 litres, so this unit describes the slow, sustained flows that matter over the length of a working day rather than a minute.
Fuel consumption is its most durable use. A boat's diesel engine burns 1 to 5 gallons per hour at cruising speed, a generator 0.5 to 2, and an agricultural tractor 2 to 4. Because such engines run at steady load for hours, the hourly figure multiplied by the hours of running gives the fuel bill directly, which is why boat and plant operators still think in these terms.
Oil-fired heating uses the unit for burner nozzles. A domestic oil boiler is fitted with a nozzle rated in gallons per hour — 0.5, 0.65 or 0.85 for a house — and that rating, multiplied by the calorific value of the oil, gives the heat output. Changing the nozzle changes the output, so the nozzle size on the burner label is effectively the rating of the appliance.
Water treatment and dosing are described the same way. A softener's regeneration flow, a chlorinator's feed rate and a chemical dosing pump on a cooling system are all set in gallons per hour, chosen so that the treated water leaves the plant with the concentration the process requires over a whole shift.
Older domestic water fittings carried the unit too. A header tank's fill rate, a cistern's refill and a slow-running standpipe were measured in gallons per hour in British practice, and the same figure told a householder how long a tank would take to recover after a bath had emptied it.
For scale, one gallon per hour is about 4.5 litres per hour, and 220 gallons per hour is about a cubic metre per hour. A rate of one gallon per hour would fill a domestic bath in about eighty hours, which is a fair reminder that this unit measures processes, not deliveries.
One gallon per hour equals about 4.546 litres per hour, about 0.004546 cubic metres per hour, or about 1.201 US gallons per hour.
| Unit | Symbol | 1 Gallon per hour equals | 1 of these equals | Converter |
|---|---|---|---|---|
| Milliliter per second | mL/s | 1.26280277778 mL/s | 0.791889293877 gal/h | Gallons per hour to Milliliters per second |
| Milliliter per minute | mL/min | 75.7681666667 mL/min | 0.0131981548979 gal/h | Gallons per hour to Milliliters per minute |
| Milliliter per hour | mL/h | 4546.09 mL/h | 0.000219969248299 gal/h | Gallons per hour to Milliliters per hour |
| Liter per second | L/s | 0.00126280277778 L/s | 791.889293877 gal/h | Gallons per hour to Liters per second |
| Liter per minute | L/min | 0.0757681666667 L/min | 13.1981548979 gal/h | Gallons per hour to Liters per minute |
| Liter per hour | L/hour | 4.54609 L/hour | 0.219969248299 gal/h | Gallons per hour to Liters per hour |
| Cubic millimeter per second | mm³/s | 1262.80277778 mm³/s | 0.000791889293877 gal/h | Gallons per hour to Cubic millimeters per second |
| Cubic millimeter per minute | mm³/min | 75768.1666667 mm³/min | 0.0000131981548979 gal/h | Gallons per hour to Cubic millimeters per minute |
| Cubic millimeter per hour | mm³/hour | 4546090 mm³/hour | 0.000000219969248299 gal/h | Gallons per hour to Cubic millimeters per hour |
| Cubic centimeter per second | cm³/s | 1.26280277778 cm³/s | 0.791889293877 gal/h | Gallons per hour to Cubic centimeters per second |
| Cubic centimeter per minute | cm³/min | 75.7681666667 cm³/min | 0.0131981548979 gal/h | Gallons per hour to Cubic centimeters per minute |
| Cubic centimeter per hour | cm³/h | 4546.09 cm³/h | 0.000219969248299 gal/h | Gallons per hour to Cubic centimeters per hour |
| Cubic meter per second | m³/s | 0.00000126280277778 m³/s | 791889.293877 gal/h | Gallons per hour to Cubic meters per second |
| Cubic meter per minute | m³/min | 0.0000757681666667 m³/min | 13198.1548979 gal/h | Gallons per hour to Cubic meters per minute |
| Cubic meter per hour | m³/h | 0.00454609 m³/h | 219.969248299 gal/h | Gallons per hour to Cubic meters per hour |
| Cubic inch per second | in³/s | 0.0770609535532 in³/s | 12.9767405397 gal/h | Gallons per hour to Cubic inches per second |
| Cubic inch per minute | in³/min | 4.62365721319 in³/min | 0.216279008995 gal/h | Gallons per hour to Cubic inches per minute |
| Cubic inch per hour | in³/h | 277.419432792 in³/h | 0.00360465014991 gal/h | Gallons per hour to Cubic inches per hour |
| Cubic foot per second | ft³/s | 0.0000445954592353 ft³/s | 22423.807651 gal/h | Gallons per hour to Cubic feet per second |
| Cubic foot per minute | ft³/min | 0.00267572755412 ft³/min | 373.730127516 gal/h | Gallons per hour to Cubic feet per minute |
| Cubic foot per hour | ft³/h | 0.160543653247 ft³/h | 6.2288354586 gal/h | Gallons per hour to Cubic feet per hour |
| Fluid ounce per second | fl oz/s | 0.0444444444444 fl oz/s | 22.5 gal/h | Gallons per hour to Fluid ounces per second |
| Fluid ounce per minute | fl oz/min | 2.66666666667 fl oz/min | 0.375 gal/h | Gallons per hour to Fluid ounces per minute |
| Fluid ounce per hour | fl oz/h | 160 fl oz/h | 0.00625 gal/h | Gallons per hour to Fluid ounces per hour |
| Gallon per second | gal/s | 0.000277777777778 gal/s | 3600 gal/h | Gallons per hour to Gallons per second |
| Gallon per minute | gal/min | 0.0166666666667 gal/min | 60 gal/h | Gallons per hour to Gallons per minute |
| US Gallon per second | gal US/s | 0.000333597201529 gal US/s | 2997.62706466 gal/h | Gallons per hour to US Gallons per second |
| US Gallon per minute | gal US/min | 0.0200158320917 gal US/min | 49.9604510777 gal/h | Gallons per hour to US Gallons per minute |
| US Gallon per hour | gal US/h | 1.2009499255 gal US/h | 0.832674184629 gal/h | Gallons per hour to US Gallons per hour |