Enter the horsepower, load (output power), and input power into the calculator to determine the motor efficiency of an electric motor.

## Motor Efficiency Formula

The following formula is used to calculate the efficiency of an electric motor.

n = .7457 * HP * L / iP *100
• Where n is the efficiency (%)
• HP is the motor horsepower (hp
• L is the load (percentage of rated power i.e .50 for 50%)
• iP is the input power (kW)

To calculate a motor efficiency, multiply the horsepower by the load ratio, divide by the input power, and finally multiply by 74.57.

## Motor Efficiency Definition

What is motor efficiency? Motor efficiency is the ratio or percentage of input power that a motor, typically an electric one, can convert into useful output work or power.

## Example Problem

How to calculate motor efficiency?

1. First, determine the input power.

For this example, we are analyzing an electric motor in a car that receives its power from a battery back. The input power is 85 kW.

2. Next, determine the maximum horsepower.

The maximum rated horsepower of the engine/motor is 150 hp.