# Pump Power Calculator

> Size a pump and estimate the electrical power it will draw at a given duty point.

Page: https://freecalculator.tech/tools/pump-power-calculator
Last reviewed: 2026-09-15

## Formula

Ph = ρ × g × Q × H; Shaft power = Ph ÷ pump efficiency; Electrical input = Shaft power ÷ motor efficiency

- Ph = ρ × g × Q × H; Shaft power = Ph ÷ pump efficiency; Electrical input = Shaft power ÷ motor efficiency.
- Inputs used: Flow rate, Flow unit, Total head, Fluid density, Pump efficiency, Motor efficiency.
- Edge handling: Flow rate is required.; Flow rate must be greater than zero.; Flow rate must be no more than 1000000000.; Total head is required.; Total head cannot be negative..

## Inputs

- Flow rate
- Flow unit
- Total head
- Fluid density
- Pump efficiency
- Motor efficiency

## Worked example: 100 m³/h of water against 30 m of head

Pump at 75% efficiency driven by a 94% efficient motor.
1. Start with Flow rate: 100, Flow unit: m3_h, Total head: 30, Fluid density: 998, Pump efficiency: 75, Motor efficiency: 94.
2. Apply the method: Ph = ρ × g × Q × H; Shaft power = Ph ÷ pump efficiency; Electrical input = Shaft power ÷ motor efficiency.
3. Pump at 75% efficiency driven by a 94% efficient motor.

## Common questions

### Where does this formula come from?

Improving Pumping System Performance: A Sourcebook for Industry, U.S. Department of Energy. See the source link on this page.

### What kind of calculation is this?

Hydraulic power from density, gravity, flow and head, divided by the efficiencies the engineer supplies. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.

### What are its limits?

Power at one duty point only. It does not model system curves, NPSH or transient behaviour.

### How do I use the Pump Power Calculator?

Enter the required values for Flow rate, Flow unit, Total head, Fluid density, Pump efficiency, and the other fields shown. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.

### What formula does the Pump Power Calculator use?

Ph = ρ × g × Q × H; Shaft power = Ph ÷ pump efficiency; Electrical input = Shaft power ÷ motor efficiency The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.

### Can the Pump Power Calculator be used for exact decisions?

Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.

## Limitations and assumptions

- Inputs outside the supported range are rejected rather than forced into a result.
- The result depends on the values you enter for this pump power calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.

## Sources

- U.S. Department of Energy — https://www.energy.gov/eere/amo/articles/improving-pumping-system-performance-sourcebook-industry-second-edition

## Cite this page

- APA: Free Calculator. (2026, September 15). Pump Power Calculator. https://freecalculator.tech/tools/pump-power-calculator
- MLA: "Pump Power Calculator." Free Calculator, 15 Sept. 2026, https://freecalculator.tech/tools/pump-power-calculator.
- Link: Pump Power Calculator — Free Calculator, https://freecalculator.tech/tools/pump-power-calculator