Construction Calculator - Water and Utility

Gallons Per Minute Calculator

Calculate gallons per minute from volume and time.

Reviewed: August 26, 2026

Calculate Gallons Per Minute

For the Gallons Per Minute Calculator, enter water volume and time. It divides the measured water volume by elapsed minutes and reports GPM, liters per minute, and gallons per hour.

Construction measuring tools arranged beside a residential building project

Formula used

Average flow rate (GPM) = measured U.S. gallons ÷ elapsed minutes

Gallons Per Minute Calculator measurement plan showing Water volume gallons, Time minutes

Worked gallons per minute example

Gallons Per Minute Calculator example: 325 U.S. gal ÷ 30 min = 10.83 GPM. That same average is 41.01 L/min or 650 gal/h.

Interpret gallons and flow

Use GPM for fixture, pump, irrigation, or transfer comparisons only when the measurement interval represents normal operation.

System effects the formula omits

Unsteady flow, inaccurate container markings, start-stop timing, pump cycling, leakage, and pressure changes affect a measured average.

Questions specific to this calculation

How should I measure a reliable flow-rate test?

Enter U.S. gallons collected or transferred and the elapsed minutes. The calculator divides volume by time and also reports liters per minute and gallons per hour.