Pump Calculator
Work out the power a pump needs for a given flow and head, and a motor size to match. Then see how flow, head and power change if you run the pump at another speed or trim the impeller.
Power and motor
Shaft power:
- Hydraulic power
- Suggested motor, with 15% margin
- Pressure rise
At the new speed and impeller
- Flow
- Head
- Shaft power
Hydraulic power = ρ × g × Q × H. Shaft power = hydraulic power ÷ pump efficiency. Affinity laws: flow changes with speed and diameter, head with their square, and power with their cube.
The affinity laws are exact for speed changes and an approximation for small impeller trims, within about 10–20%. Check against the maker's pump curve, NPSH and the motor's full-load rating before you change a duty.