Water pump power calculator
Work out what motor a pump needs from the flow rate and total head, including pump and motor efficiency.
How it is calculated
Hydraulic HP = GPM × head (ft) / 3960
Hydraulic kW = Q (m³/h) × H (m) / 367
Shaft power = hydraulic power / pump efficiency
Total dynamic head is the sum of the vertical lift, friction losses in pipes and fittings, and the pressure needed at the outlet (1 psi ≈ 2.31 ft of water).
Centrifugal pump efficiency is usually 50–80 % depending on size and duty point; electric motors 80–95 %. Pick the next standard motor above the shaft power with a 10 % margin.
Frequently asked questions
What size pump do I need for 44 GPM at 131 ft?
Hydraulic power is about 1.46 HP; at 70 % pump efficiency the shaft needs about 2.1 HP, so a 3 HP motor with margin.
What is total dynamic head?
The energy per unit weight the pump must add, expressed in feet or metres of water: lift plus friction plus final pressure.
How do I convert psi to feet of head?
Multiply by 2.31: 50 psi is about 115 ft of water.