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.