Short definition

GPM stands for gallons per minute, the standard US unit for water flow rate. One GPM equals 3.785 liters per minute. You’ll see GPM on every fixture and appliance spec — kitchen faucets at 1.5–2.2 GPM, showerheads at 1.5–2.5 GPM, tankless water heaters rated 4–11 GPM whole-house.

What it is

GPM is the practical shorthand. When a tankless water heater quote says “9 GPM unit,” that’s the maximum simultaneous flow the heater can deliver hot water to. A 9-GPM unit can handle a shower (2.5 GPM) plus a kitchen sink (2 GPM) plus a bathroom faucet (1.2 GPM) running at the same time and still meet target temperature.

For more on flow rate generally, see the dedicated Flow rate (GPM) entry.

Flow rate (GPM) · Static water pressure · Friction loss · Pressure gauge