| Gallons per hour (gal/h) | Milliliters per second (mL/s) |
|---|---|
| 1 Gallon per hour | 1.26280277778 mL/s |
| 2 Gallons per hour | 2.52560555556 mL/s |
| 3 Gallons per hour | 3.78840833333 mL/s |
| 4 Gallons per hour | 5.05121111111 mL/s |
| 5 Gallons per hour | 6.31401388889 mL/s |
| 10 Gallons per hour | 12.6280277778 mL/s |
| 20 Gallons per hour | 25.2560555556 mL/s |
| 25 Gallons per hour | 31.5700694444 mL/s |
| 50 Gallons per hour | 63.1401388889 mL/s |
| 100 Gallons per hour | 126.280277778 mL/s |
| Reference | Gallons per hour (gal/h) | Milliliters per second (mL/s) |
|---|---|---|
| A domestic shower | 118.783 gal/h | 150 mL/s |
| A kitchen tap | 131.982 gal/h | 166.667 mL/s |
| A garden hose | 197.972 gal/h | 250 mL/s |
| The Amazon river | 1.65505 × 1011 gal/h | 2.09 × 1011 mL/s |
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 millilitre per second is a unit of volumetric flow rate equal to one millilitre of fluid passing a point every second. Its symbol is mL/s. Since a millilitre is a cubic centimetre, the unit is identical to the cubic centimetre per second, and the two names are used interchangeably depending on whether the fluid is thought of as a liquid or as a volume of space.
Volumetric flow rate is a volume divided by a time, so it has the dimensions of length cubed per second. That makes it convertible to any other flow unit by a single multiplication, and it also means that a flow rate multiplied by a duration gives the total volume delivered — the arithmetic that underlies every dosing calculation and every water bill.
A millilitre per second is a small but visible flow. A tap dripping steadily produces perhaps a tenth of this; a thin stream from a partly opened tap is a few millilitres per second; a garden hose at full flow is several hundred. In household terms it is the rate at which a teaspoon fills in about five seconds.
The unit belongs to the laboratory and to small machinery. Peristaltic pumps, dosing systems, fuel injectors and analytical instruments all work in this range, and their specifications are written in millilitres per second when the process is fast and in millilitres per minute when it is slow. Where a pump must deliver a precise quantity, the rate and the running time together define the dose.
Human physiology gives useful comparisons. Resting cardiac output is about eighty millilitres per second, urine production averages under a fiftieth of that, and saliva production is around a hundredth. The flow through a single capillary is far smaller still and is measured in cubic millimetres per hour.
Converting to the SI base unit requires care with the powers of ten. One millilitre per second is a millionth of a cubic metre per second, because a millilitre is a millionth of a cubic metre. That factor of a million between the practical unit and the base unit is why flow rates are almost never quoted in cubic metres per second outside hydrology and heavy engineering.
One millilitre per second equals 0.001 litres per second, 60 millilitres per minute, or about 0.0000353 cubic feet per second.