US Gallon per second (gal US/s)

The US gallon per second is a unit of volumetric flow rate equal to one United States gallon passing a point every second. Its symbol is gal US/s. The US gallon is exactly 3.785411784 litres, descended from the English wine gallon of 231 cubic inches, so one US gallon per second is a little under four litres every second.

Fire protection in the United States works at this scale. A fire hydrant flows several gallons per second, a pumper truck delivers 20 or more, and a large sprinkler system's design demand runs to tens. Fire codes state these figures in gallons per minute, but hydraulic calculations of friction loss in the mains use the per-second value, and the two are the same number divided by sixty.

Municipal water and wastewater engineering also reaches it. A neighbourhood water main carries a few gallons per second at peak hour, a lift station handles tens, and a treatment plant's influent hundreds. American practice usually states plant capacity in million gallons per day, and one gallon per second is 0.0864 million gallons per day — a conversion any water engineer performs from memory.

Industrial cooling and process water are described here as well. Condenser cooling water, quench flows and washdown systems all reach gallons per second, and the pump power required follows from the flow multiplied by the head, so an increase in flow of ten per cent shows up directly on the electricity bill.

The difference from the imperial gallon deserves a clear statement. The US gallon is about 17 per cent smaller than the imperial one, so the same numerical rate is a materially different flow on either side of the Atlantic. Equipment documentation should say which gallon it means, and prudent engineers convert to litres before comparing anything.

For scale, one US gallon per second is about 3.79 litres per second, and 0.264 US gallons per second is one litre per second. A flow of ten US gallons per second is nearly 38 litres per second, enough to fill a domestic bath in three seconds and comparable to a small stream.

One US gallon per second equals about 3.785 litres per second, about 0.003785 cubic metres per second, or about 0.8327 imperial gallons per second.

US Gallon per second conversion table