Work out hydraulic pump flow instantly with clear inputs, formula shown and shareable results.
A positive displacement pump moves its displacement once per revolution, so theoretical flow is displacement times speed divided by 231 cubic inches per gallon. Volumetric efficiency accounts for internal slip past clearances, which rises with pressure and with oil temperature as viscosity falls.
Pump flow
GPM = displacement in³/rev x rpm / 231 x volumetric efficiency
GPM = displacement in³/rev x rpm / 231 x volumetric efficiency. A positive displacement pump moves its displacement once per revolution, so theoretical flow is displacement times speed divided by 231 cubic inches per gallon.
Clearances open up, so more oil slips back internally at pressure. A drop in volumetric efficiency at rated pressure is the standard wear test for a hydraulic pump.
This calculator takes 3 inputs: Pump displacement, Drive speed, Volumetric efficiency. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.