Fundamentals
PSI vs GPM: Why Pressure Is Not Flow
Understand the difference between water pressure and flow rate before choosing a calculator.
PSI to GPM Editorial Team ·
Pressure and flow describe different properties of a water system. PSI measures pressure, while GPM measures volume moving per minute.
The missing system
The same pressure can produce dramatically different flow through a small nozzle, a long hose, or a large smooth pipe. Diameter, length, roughness, elevation, and restrictions determine how pressure becomes flow.
Choose the physical model
Use an orifice equation for a short outlet, a K-factor for a listed sprinkler, Cv for a valve, and a friction model for a pipe run. Field measurement remains the best check of the complete assembled system.