Calculate Motor Efficiency
Enter motor input power and useful output power below.
What Is a Motor Efficiency Calculator?
A motor efficiency calculator determines how effectively an electric motor converts supplied electrical power into useful mechanical output power. It compares motor output power with motor input power and expresses the result as a percentage.
The calculator also determines the amount of power lost during the conversion process. These losses can include electrical, magnetic, mechanical, and other internal motor losses.
Motor Efficiency Formula
Motor efficiency is calculated by dividing useful mechanical output power by electrical input power and multiplying by 100.
Here, η represents efficiency, Pout is useful motor output power, and Pin is electrical input power. Both power values must be expressed using the same base unit before the ratio is calculated.
How to Use the Motor Efficiency Calculator
- Enter the electrical input power supplied to the motor.
- Choose the input power unit, such as W, kW, MW, or HP.
- Enter the useful mechanical output power of the motor.
- Select the correct output power unit.
- Click Calculate Motor Efficiency.
The calculator automatically converts both values into watts before calculating efficiency, power loss, and related values.
Motor Efficiency Calculation Example
Suppose an electric motor consumes 5.5 kW of electrical input power and delivers 5 kW of useful mechanical output power.
η = 0.9091 × 100
η ≈ 90.91%
The motor converts approximately 90.91% of its input power into useful mechanical output, while the remaining power is lost through heat, friction, electrical resistance, and other motor losses.
How to Calculate Motor Power Loss
Motor power loss is the difference between electrical input power and useful mechanical output power.
For a motor with 5.5 kW input and 5 kW output, the calculated loss is 0.5 kW or 500 watts.
Where Does Motor Power Get Lost?
Electrical Losses
Current flowing through motor windings creates resistive losses. These losses are commonly associated with winding resistance and appear mainly as heat.
Magnetic Losses
Motor cores experience magnetic losses related to changing magnetic fields. These losses can include hysteresis and eddy-current effects.
Mechanical Losses
Bearings, friction, cooling fans, and air resistance consume some mechanical energy and reduce the useful output available at the motor shaft.
Input Power vs Output Power
Input power is the electrical energy supplied to a motor, while output power is the useful mechanical power available at the shaft. In a real motor, output power is normally less than input power because some energy is lost.
Efficiency indicates what proportion of the supplied input power reaches the motor shaft as useful output.
Motor Efficiency as a Decimal and Percentage
Efficiency may be written as either a decimal or percentage. For example, an efficiency ratio of 0.90 is equivalent to 90%.
90% ÷ 100 = 0.90
This calculator displays both values so they can be used easily in other electrical and motor formulas.
Motor Horsepower and Kilowatts
Motor output ratings are commonly expressed in horsepower or kilowatts. This calculator accepts either unit and converts the value automatically.
1 kW = 1,000 W
When comparing motor input and output values, converting both to the same unit is necessary before calculating efficiency.
Why Motor Efficiency Matters
Higher efficiency means a greater portion of electrical input power is converted into useful mechanical work. Improved efficiency can reduce energy losses and operating costs when a motor runs for extended periods.
However, motor efficiency varies with motor type, size, design, speed, and load. For exact equipment performance, manufacturer data and standardized test results should be used.
Common Motor Efficiency Units
| Quantity | Symbol | Common Units |
|---|---|---|
| Input Power | Pin | W, kW, MW, HP |
| Output Power | Pout | W, kW, MW, HP |
| Power Loss | Ploss | W, kW, MW |
| Efficiency | η | % or Decimal |
Frequently Asked Questions
How do you calculate motor efficiency?
Divide useful mechanical output power by electrical input power and multiply by 100. The formula is η = (Pout / Pin) × 100%.
What is motor input power?
Motor input power is the electrical power supplied to the motor before losses occur. It is greater than useful output power in a real operating motor.
What is motor output power?
Motor output power is the useful mechanical power produced at the motor shaft after internal electrical and mechanical losses.
How do you calculate motor power loss?
Subtract motor output power from motor input power. The formula is Ploss = Pin − Pout.
Can motor efficiency be greater than 100%?
No. A real motor cannot produce more useful output power than the energy supplied to it. An efficiency result above 100% usually indicates incorrect or inconsistent input data.
Can I use horsepower in this calculator?
Yes. The calculator supports horsepower and automatically converts it using approximately 746 watts per mechanical horsepower.
Why is motor output power lower than input power?
Some electrical energy is lost through winding resistance, magnetic effects, friction, bearings, cooling, and other motor losses, so useful output is lower than input.