Hydraulic Pump Flow Calculator
Find pump flow, displacement or RPM with volumetric efficiency.
Results
Actual flow
- Theoretical flow
- 30 L/min0.5 L/s7.93 US GPM
Use volumetric efficiency for the specified pressure, fluid and speed. This calculation does not determine allowable pressure, operating speed, cavitation limits or required shaft power. A zero-flow reverse result is a mathematical zero-demand value, not a pump selection.
Formula · How it works
Formula
Qₜₕ = Vg × n / 60; Q = Qₜₕ × ηᵥVg = Q × 60 / (n × ηᵥ)n = Q × 60 / (Vg × ηᵥ)Theoretical Qₜₕ = Vg × n/60 in m³/s when displacement Vg is m³/rev and n is rpm. Actual Q = Qₜₕηᵥ. In practical units, Q(L/min) = Vg(cc/rev) × n(rpm) × ηᵥ/1000. Inverse formulas are Vg = 60Q/(nηᵥ) and n = 60Q/(Vgηᵥ). One cc is one cm³; GPM means US gallons per minute.
Worked example
A 20 cc/rev pump at 1,500 rpm has a theoretical flow of 30 L/min. At 90% volumetric efficiency, actual flow is 27 L/min (0.45 L/s). Reversing those inputs gives 20 cc/rev or 1,500 rpm.
How it works
Geometric displacement is the fluid volume swept each revolution. Multiplying it by rotational speed gives theoretical flow. Volumetric efficiency reduces this to an estimate of delivered flow by accounting for internal leakage.
Common questions
Why are actual and theoretical flow different?
Theoretical flow assumes each revolution delivers the full geometric displacement. Leakage reduces delivered flow, represented by volumetric efficiency.
Can I solve for pump displacement or speed?
Yes. Select Displacement or Pump speed and enter desired actual flow and volumetric efficiency. Displacement mode requires positive RPM; speed mode requires positive displacement.