# Pump Efficiency Calculator

> Calculate pump efficiency step by step: η = ρ g Q H ÷ P_shaft.

Page: https://freecalculator.tech/tools/pump-efficiency-calculator
Last reviewed: 2026-11-03

## Formula

η = ρ g Q H ÷ P_shaft.

- Uses shaft power; with electrical input power the result is wire-to-water efficiency.
- Results above 100% indicate a measurement error.
- All inputs must be above zero.
- η = ρ g Q H ÷ P_shaft.
- Inputs used: Measured flow, Measured total head, Fluid density, Measured shaft power.

## Inputs

- Measured flow
- Measured total head
- Fluid density
- Measured shaft power

## Pump efficiency formula

Efficiency = hydraulic power / shaft power. Hydraulic power = density x g x flow x head. With flow in L/s and head in m, kW = density x 9.80665 x (flow / 1,000) x head / 1,000.

## Pump efficiency vs wire-to-water efficiency

Using shaft power gives the efficiency of the pump alone. Using electrical input power instead gives the overall efficiency of motor, drive and pump together, which is always lower.

## Why field results differ from the curve

Wear, running away from the best efficiency point and measurement error all lower field efficiency. Errors in flow or head change the result in proportion, so use calibrated instruments.

## Worked example: 10 L/s at 25 m head, water

1. Hydraulic power = 1,000 x 9.80665 x 0.010 x 25 / 1,000 = 2.45 kW
2. Efficiency = 2.45 / 3.5 kW shaft = about 70%

## Common questions

### Why is my pump less efficient than the catalogue?

Wear, operating away from the best efficiency point, and measurement accuracy all reduce field efficiency.

### What if I only know electrical power?

Enter it as shaft power and read the result as overall (wire-to-water) efficiency.

### How accurate must measurements be?

Small errors in flow or head change efficiency proportionally, so use calibrated instruments.

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

Enter the required values for Measured flow, Measured total head, Fluid density, Measured shaft power. 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 Efficiency Calculator use?

η = ρ g Q H ÷ P_shaft. 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.

### Can the Pump Efficiency 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

- Single operating point.
- Measurement uncertainty not propagated.
- Assumes steady conditions.
- Results are estimates for planning and learning. Real designs, installations and bids must be checked by a qualified, licensed professional against the codes that apply where you work.
- The result depends on the values you enter for this pump efficiency 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, November 3). Pump Efficiency Calculator. https://freecalculator.tech/tools/pump-efficiency-calculator
- MLA: "Pump Efficiency Calculator." Free Calculator, 3 Nov. 2026, https://freecalculator.tech/tools/pump-efficiency-calculator.
- Link: Pump Efficiency Calculator — Free Calculator, https://freecalculator.tech/tools/pump-efficiency-calculator