Three practical calculations for sizing or cross-checking a pump — flow from displacement, required power, or achievable flow from available power.
Flow (LPM) = Displacement (cc/rev) × RPM ÷ 1000
Power (kW) = Flow (LPM) × Pressure (bar) ÷ 600 ÷ Efficiency
This is the input power your engine/motor needs to deliver — not the theoretical hydraulic output, which is lower.
Flow (LPM) = Power (kW) × Efficiency × 600 ÷ Pressure (bar)
Useful for checking whether your engine can realistically drive a pump at your target pressure.
Overall pump efficiency (volumetric × mechanical) typically runs 85-90% for a well-maintained piston pump, lower for gear pumps or a worn unit. If you're not sure, 88% is a reasonable working estimate for a healthy piston pump.
Use these figures as a planning reference, not an exact specification — actual pump and system performance depends on factors like oil viscosity, temperature, and system design beyond what a simple calculator can account for. For matching an exact replacement, see our Which Pump Do I Need tool or WhatsApp us your machine details.