PSI to GPM Calculator

Estimate water flow rate in gallons per minute from nozzle pressure and orifice diameter, using the standard discharge formula. An estimate, not a guarantee.

Estimated flow

51.2 GPM

Litres per minute—

Gallons per hour—

Orifice area—

Flow vs. pressure

Flow rises with the square root of pressure, doubling flow needs four times the pressure.

How it works

Pressure and flow are not the same thing, so there is no direct PSI-to-GPM conversion. Instead, flow through a nozzle is estimated from the pressure and the size of the opening. Flow scales with the square root of pressure, so it grows more slowly than pressure.

GPM = 29.84 × Cd × d² × √PSI
d = orifice diameter (inches), Cd = discharge coefficient

Worked example

A 0.5-inch smooth nozzle (Cd 0.97) at 50 PSI gives 29.84 × 0.97 × 0.25 × √50 ≈ 51 GPM.

Frequently asked questions

Can you convert PSI directly to GPM?

No, flow depends on the opening size too. This tool uses the discharge formula with pressure and diameter.

What is the discharge coefficient?

Cd captures losses and flow contraction, about 0.97 for a smooth nozzle, lower for sharp orifices.