What Is the Formula to Calculate GPM?

The U.S. Army/CC-BY-2.0

Gallons per minute, abbreviated as GPM, can be calculated by the formula dividing the amount of flow in gallons by the unit of time in minutes. This value is also known as the fluid flow rate and may be represented by the variable Q.

Gallons per minute can also be calculated by multiplying the horsepower by 1,714 and dividing the product by the fluid pressure. For fluid motor torque, the formula is the torque times the rotations per minute, divided by 36.77 times the pressure. Pump output flow in terms of gallons per minute can be found by multiplying the speed in rotations per minute by the displacement in cubic inches divided by 231.