👤 By Why Calculator Team ✔ Reviewed by Matt Le (Founder of Why Calculator) 📅 Last Updated April 12, 2026
Motor Efficiency Calculator
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Looking for a reliable way to calculate motor efficiency? Our Motor Efficiency Calculator helps you determine motor efficiency using simple and advanced methods. Whether you have input and output power values or need to calculate efficiency using voltage, current, power factor, torque, and RPM, this tool has you covered.
Just enter the required values, and the calculator will instantly provide accurate efficiency results. Perfect for engineers, technicians, and anyone working with electric motors!
How to Calculate Motor Efficiency?
Motor efficiency (η) is a measure of how effectively a motor converts electrical power into mechanical power. It is expressed as a percentage and is calculated using the following formula:
Formula for Motor Efficiency
η = (Output Power / Input Power) × 100
Where:
- η = Efficiency (%)
- Output Power = The mechanical power delivered by the motor (Watts or HP)
- Input Power = The electrical power consumed by the motor (Watts)
Example 1:
- Given:
- Input Power = 2000 W
- Output Power = 1800 W
η = (1800 / 2000) × 100 = 90%
Example 2: Efficiency Using Voltage, Current, and Power Factor
If the motor operates at 230V, draws 10A, and has a power factor of 0.85, and the output power is 1800 W:
Input Power:
Pinput = V × I × Power Factor
Pinput = 230 × 10 × 0.85
= 1955W
Efficiency:
η = (1800 / 1955) × 100
= 92.07%
What is Normal Motor Efficiency?
The normal efficiency of a motor depends on its type, size, and application. Typically, motor efficiency ranges from 70% to 98%. Here’s a general breakdown:
Efficiency by Motor Type:
- Standard AC Motors: 75% – 90%
- High-Efficiency (Premium) Motors: 90% – 97%
- Small Motors (<1 HP): 50% – 75%
- Large Industrial Motors (>50 HP): 95% – 96%
- DC Motors: 70% – 85%
Factors Affecting Motor Efficiency:
- Motor Size – Larger motors generally have higher efficiency.
- Load Condition – Motors are most efficient when running at 75% – 100% of rated load.
- Motor Design – Premium efficiency motors are designed with better materials and windings.
- Maintenance – Proper lubrication and cooling improve efficiency.
Reference:
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