| Gallons per hour (gal/h) | Liters per hour (L/hour) |
|---|---|
| 1 Gallon per hour | 4.54609 L/hour |
| 2 Gallons per hour | 9.09218 L/hour |
| 3 Gallons per hour | 13.63827 L/hour |
| 4 Gallons per hour | 18.18436 L/hour |
| 5 Gallons per hour | 22.73045 L/hour |
| 10 Gallons per hour | 45.4609 L/hour |
| 20 Gallons per hour | 90.9218 L/hour |
| 25 Gallons per hour | 113.65225 L/hour |
| 50 Gallons per hour | 227.3045 L/hour |
| 100 Gallons per hour | 454.609 L/hour |
| Reference | Gallons per hour (gal/h) | Liters per hour (L/hour) |
|---|---|---|
| A domestic shower | 118.783 gal/h | 540 L/hour |
| A kitchen tap | 131.982 gal/h | 600 L/hour |
| A garden hose | 197.972 gal/h | 900 L/hour |
| The Amazon river | 1.65505 × 1011 gal/h | 7.524 × 1011 L/hour |
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.
The litre per hour is a unit of volumetric flow rate equal to one litre passing a point every hour. Its symbol is L/h. It is the unit of slow, sustained flows — the ones too gradual to watch, where what matters is how much has moved by the end of a working day rather than what the stream looks like now.
Irrigation is its clearest home. A drip emitter is rated at 2, 4 or 8 litres per hour, and an orchard is designed by counting emitters: two hundred trees with two 4-litre emitters each draw 1,600 litres per hour, so a three-hour watering delivers 4.8 cubic metres. Because the emitters run for hours, the hourly figure is the one that maps directly onto the water budget.
Fuel consumption is quoted the same way whenever an engine runs at a steady load rather than travelling. A generator burns 2 to 5 litres per hour, a farm tractor 10 to 20, a large marine diesel several thousand. Litres per hour is the honest unit for these machines because litres per 100 kilometres means nothing to something that does not move.
Heating appliances follow. An oil boiler is rated by its burner nozzle in litres per hour, typically 1.5 to 3 for a house, and the figure multiplied by the heating value of the oil gives the heat output in kilowatts. A hot-water tap that produces 8 litres per minute is 480 litres per hour, which is why the same equipment carries both numbers in different parts of its documentation.
Laboratory and process work uses the unit for pumps that must run all day. Peristaltic dosing pumps for chlorination, water treatment and fermentation feeds are specified in litres per hour, often with a turndown range like 0.5 to 20, because the point of such a pump is to keep a slow rate constant for weeks.
Leaks and losses are described here too. A dripping tap loses a few litres per hour, which is trivial in a minute and a hundred litres by the next morning. Water utilities express network losses this way for the same reason: a slow rate compounded over the hours of a year is what turns an unnoticed defect into a measurable volume.
One litre per hour equals about 0.000278 litres per second, 0.01667 litres per minute, or 0.001 cubic metres per hour.