Mechanical calculations, kept preliminary
A mechanical figure on this site answers one equation. Pump power is ρgQH. Shaft power is torque times angular speed. Neither selects a machine.
What to do with the number
Use it to see whether a duty is in the right order: a few kilowatts, or tens. Then open the manufacturer curve. The curve carries NPSH, efficiency at that duty, and the motor frame. This site does not.
Worked duty
0.02 m³/s through 15 m of head, water, 70% pump efficiency, is 2.94 kW hydraulic and 4.20 kW at the shaft. A 5.5 kW motor might be the next question. It is not the answer. Starting current, service factor and the system curve still sit outside the equation.
Open the pump power calculator or the shaft power calculator.
Last checked 2 October 2026. Original guidance. Standards text stays with the publisher.