Pump Power Calculator
Calculate the hydraulic power a pump delivers and the shaft and electrical power it needs, from flow and either head or differential pressure.
- Ph = ρ × g × Q × H = 998.2 × 9.807 × 0.02778 × 50 = 13.6 kW
- Pshaft = Ph ÷ ηpump = 18.13 kW
- Pmotor = Pshaft ÷ ηmotor = 19.28 kW
Pump Power Formulas
Pshaft = Ph ÷ ηpump
Pmotor = Pshaft ÷ ηmotor
Q is the flow in m³/s, H the total head in metres of the pumped liquid, ρ the density, g = 9.80665 m/s² and ΔP the pressure rise in Pa. Efficiencies are fractions. Select the motor with a margin above the shaft power at the worst operating point.
Worked example
100 m³/h of water against 50 m head: Ph = 998.2 × 9.807 × 0.02778 × 50 = 13.6 kW. At 75 % pump efficiency the shaft needs 18.1 kW and the motor draws about 19.3 kW.
Frequently Asked Questions
What is the difference between hydraulic and shaft power?
Hydraulic power is the energy given to the liquid. Shaft (brake) power is what the pump needs at its shaft, which is higher because of pump losses.
Head or pressure: which should I use?
Either. Head in metres is independent of density; pressure already includes density. They are linked by ΔP = ρgH.
How much motor margin is usual?
Motor sizing margins come from company standards and pump standards; check the end of curve power, not just the duty point.
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