Pump power calculator
Helps size a pump motor for a tank, well or irrigation line. Enter the flow, total head and efficiency.
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How to use it
- Enter flow rate, total head, fluid density and pump efficiency.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Hydraulic power = ρ × g × Q × H with g = 9.80665 m/s². Shaft power = hydraulic power ÷ efficiency. 1 mechanical hp = 745.7 W.
Example
Inputs: Flow rate = 36 m³/h, Total head = 20 m, Fluid density = 1,000 kg/m³, Pump efficiency = 70 %. Result: Pump shaft power: 2.802 kW; Hydraulic power: 1.961 kW; Shaft power in horsepower: 3.757 hp.
Limits and caveats
- Does not include motor efficiency, so the electrical input is higher.
- Total head must include friction losses in pipes and fittings, not just the height difference.
Questions about this tool
What is total head?
The height from the suction level to the discharge point plus friction losses and any required outlet pressure expressed in metres.
What is the difference between hydraulic and shaft power?
Hydraulic power is the energy the liquid gains. Shaft power is higher because the pump loses some to friction and leakage.
Which motor should I pick?
Choose a motor rated above the calculated shaft power, with the safety margin the pump maker recommends.