🚿 PSI to GPM Calculator
Estimate the flow rate (GPM) through a nozzle or orifice from its pressure (PSI) and orifice diameter, using the standard orifice discharge formula.
How PSI relates to flow rate (GPM)
Pressure (PSI) and flow rate (GPM) are not directly interchangeable units — they’re related through the physical size of the opening the liquid flows through. This calculator uses the standard orifice/nozzle discharge formula: GPM = 29.84 × Cd × d² × √PSI, where d is the orifice diameter in inches and Cd is the discharge coefficient, which accounts for friction and turbulence losses at the opening.
A discharge coefficient of about 0.6 to 0.65 is typical for a sharp-edged orifice such as a nozzle or spray tip, while smoother, rounded openings can have a coefficient closer to 0.9-0.98. This formula is widely used for estimating flow through pressure washer nozzles, irrigation emitters, and fire sprinkler orifices.
This tool provides an engineering estimate for general planning purposes; actual flow rates from specific manufactured nozzles can vary and should be confirmed against the manufacturer’s rated flow chart when precision matters.