Pressure · flow · hydraulics
PSI to GPM Calculator | Flow Rate & Water Pressure Charts
Convert water pressure (PSI & Bar) to flow rate (GPM & L/min) across pipe sizes, nozzles, and orifices. Accurate hydraulics engineering formulas and instant field tables.
Fluid Mechanics Principle
Can you convert PSI directly to GPM?
No, you cannot directly convert PSI to GPM with a single conversion multiplier. PSI (Pounds per Square Inch) measures internal fluid pressure or potential energy, while GPM (Gallons per Minute) measures volumetric flow rate over time. To calculate GPM from PSI, you must know the physical conduit delivering the water—specifically the pipe inside diameter, nozzle orifice size, friction coefficient, or valve flow rating.
For example, an identical 50 PSI (3.5 bar) supply produces only 0.08 GPM (0.3 L/min) through a high-pressure misting nozzle, but delivers over 650 GPM (2,460 L/min) through an open 2.5-inch fire hydrant nozzle. Select your system component above to calculate accurate flow rates.
01 System-first models 02 Unit-aware inputs 03 Assumptions shown 04 Practical limits
Calculation desk
Tools organized by the system you are working on
Move from a field measurement to the correct model, then inspect the formula, assumptions, and practical limits.
Pipe systems
Pumps and wells
Fire protection
Valves & irrigation
Pressure washing & units
Method first
How PSI to GPM works
Identify the system
Choose pipe, nozzle, sprinkler, valve, hose, hydrant, or pump.
Enter physical inputs
Use actual dimensions, differential pressure, and applicable coefficients.
Inspect the result
Review the formula, unit convention, assumptions, and limitations.
Model selection
Choose the right pressure-to-flow method
SystemInformation neededMethod
Long pipePressure, diameter, length, materialHazen-Williams
Open nozzlePressure and opening diameterOrifice discharge
SprinklerPressure and manufacturer K-factorK-factor flow
ValvePressure drop, Cv, specific gravityValve sizing
HydrantPitot pressure, outlet, coefficientHydrant discharge
Editorial standard
Useful answers need visible limits.
Each tool names its model, units, assumptions, and intended use. Treat the result as a practical estimate, then verify safety-sensitive work with the appropriate professional or manufacturer data.
Frequently asked questions
Pressure and flow, clarified
How many GPM is 40 PSI?
There is no direct conversion between 40 PSI and GPM. PSI measures fluid pressure (potential energy), while GPM measures volumetric flow rate. Flow depends on the conduit geometry: 40 PSI through a misting nozzle yields under 0.1 GPM, through a 1/2-inch garden hose yields 6 to 12 GPM, and through an open 2.5-inch hydrant produces over 580 GPM.
Does higher PSI always mean higher GPM?
Within an identical, fixed physical piping or nozzle system, increasing pressure increases flow rate proportional to the square root of differential pressure. However, across different systems, conduit diameter and orifice size have a much greater impact than pressure.
Which pressure reading should I use?
Use the differential pressure (ΔP) across the specific component. For pipe friction loss, use available dynamic head loss along the pipe run. For hydrants and nozzles, use dynamic pitot pressure. For control valves, use net valve pressure drop.
Is US GPM different from Imperial GPM?
Yes. One US GPM equals 3.7854 L/min (0.227 m³/h). One Imperial (UK) GPM equals 4.5461 L/min (0.273 m³/h). Our calculators display both US GPM and international metric Liters per Minute (L/min) to prevent dimensional errors.