Motor Efficiency Calculator

Summary

Enter motor input power and output shaft power to instantly calculate efficiency percentage and power loss.

How it works

1. Select the power unit — watts (W) or kilowatts (kW).
2. Enter the motor input power (electrical power drawn from the supply).
3. Enter the output shaft power (mechanical power delivered by the motor).
4. The calculator applies Efficiency = (P_out / P_in) × 100 and displays the result.
5. Power loss (P_in − P_out) and loss percentage are shown alongside efficiency.
6. Switch the unit selector to convert between watts and kW at any time.

Use cases

• Verify nameplate efficiency claims against measured input and output power.
• Calculate power loss in a motor to size cooling or thermal management.
• Compare efficiency across multiple motors during equipment selection.
• Determine energy savings when replacing an old motor with a higher-efficiency model.
• Audit industrial motor loads for energy management programs.
• Compute shaft power when only input power and rated efficiency are known.
• Estimate annual energy cost of motor losses at a given run-time.

Frequently Asked Questions