Pump Power Calculator
Calculate hydraulic, shaft and motor power for a pump duty.
Please note: These are idealised textbook models using representative material data. They are for study, sizing and sanity-checking only — never for final design. Real engineering requires code-compliant analysis, verified material certificates and a qualified engineer’s sign-off.
What the Pump Power Calculator does
A pump’s useful output is the weight of fluid it lifts per second multiplied by the height it lifts it — that is hydraulic power. Dividing by pump efficiency gives the shaft power the motor must deliver, and dividing again by motor efficiency gives what the electricity meter sees.
Formula
Hydraulic power = ρ g Q HShaft power = Hydraulic power ÷ Pump efficiencyElectrical power = Shaft power ÷ Motor efficiencyH = Δp ÷ (ρ g)
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Fluid | one of 7 options | Yes | — |
| Flow rate | L/s | Yes | Accepts more than 0. |
| Duty given as | one of 2 options | Yes | — |
| Total head | number | In some modes | Shown Duty given as is Total head in metres. |
| Total head unit | one of 9 options | In some modes | Shown Duty given as is Total head in metres. |
| Pressure rise | number | In some modes | Shown Duty given as is Pressure rise. |
| Pressure rise unit | one of 7 options | In some modes | Shown Duty given as is Pressure rise. |
| Pump efficiency | % | Yes | — |
| Motor efficiency | % | Optional | — |
| Running hours per day | number | Optional | Accepts 0 or more, up to 24. |
| Electricity rate per kWh | selected currency | Optional | Accepts 0 or more. |
| Currency | one of 10 options | Optional | — |
How to use it
- Choose Fluid and Duty given as.
- Enter Flow rate and Pump efficiency.
- Fill in the remaining inputs the form shows for your choice.
- Optionally add Motor efficiency, Running hours per day and Electricity rate per kWh.
- Select Calculate.
Worked example
Pumping 10 L/s of water to 20 m of head at 70% pump efficiency.
- Flow
- 10 L/s
- Head
- 20 m
- Pump efficiency
- 70%
Hydraulic power = 998.2 × 9.807 × 0.01 × 20 = 1,958 W. At 70% the shaft needs 2.80 kW, and at 90% motor efficiency the supply must deliver 3.11 kW.
Frequently asked questions
Why quote pump duty in metres rather than pressure?
Head is independent of fluid density, so one curve describes the pump on any liquid. Pressure would change with every fluid it handles.
How much does efficiency matter?
Enormously over a pump’s life. Energy typically dwarfs purchase price, so five points of efficiency can outweigh a substantial difference in capital cost.
Method and sources
Method. Hydraulic power as ρgQH, divided by pump and motor efficiency to give shaft and electrical input power.
Assumptions
- The head entered is total dynamic head including static lift and friction losses, and efficiency applies at the duty point.
Limitations
- Pump efficiency varies across the curve and falls away from the best efficiency point. Using a single figure overstates performance for a pump operating off-duty.
- The static lift alone is not the head — omitting friction and fitting losses is the most common way this calculation comes out low.
- Operating far from the best efficiency point causes recirculation and cavitation risk, neither of which a power calculation reveals.
Sources
- The hydraulic power relationship, with the pump curve for the specific machine — Classical fluid mechanics; curve varies by manufacturer. The power relationship. Efficiency at the actual duty point must come from the manufacturer's curve.