Motor Sizing Calculator

Choosing the right motor for a mechanical system requires balancing torque, speed, inertia, and electrical parameters — the Motor Sizing Calculator works through all of it at once. Enter your required torque, operating speed, load inertia, and acceleration time, then set your supply voltage, motor efficiency, power factor, and phase configuration. You'll get the required motor power in kW and HP, along with acceleration torque, total peak torque, and full load current.

Nm

Continuous torque needed to overcome friction and external loads

RPM

Desired motor operating speed during normal operation

kg·m²

Total load inertia including gears and connected equipment

s

Time required to accelerate from 0 to operating speed

V
%

Results

Required Motor Power

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Required Horsepower

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Acceleration Torque

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Total Peak Torque

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Full Load Current

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Frequently Asked Questions

How do I determine the required torque for my application?

Required torque depends on the load characteristics, friction, and external forces. For rotating loads, calculate torque needed to overcome friction and maintain constant speed. For linear loads, convert force requirements to torque using the radius of pulleys or screws.

What is the difference between continuous torque and peak torque?

Continuous torque is the steady-state torque required during normal operation. Peak torque includes both continuous torque and acceleration torque needed during startup or speed changes. Motors must be sized to handle peak torque without overheating.

How does load inertia affect motor sizing?

Higher load inertia requires more torque to accelerate and decelerate the system. This affects the peak torque requirement and influences the motor size selection, especially for applications with frequent starts and stops.

What motor efficiency should I use in calculations?

Motor efficiency typically ranges from 85-95% for standard motors and up to 97% for premium efficiency motors. Use manufacturer specifications when available, or conservative estimates of 90% for general calculations.

How do I choose between single-phase and three-phase motors?

Three-phase motors are preferred for powers above 2-3 HP due to better efficiency, smoother operation, and lower current draw. Single-phase motors are suitable for smaller applications and where three-phase power is not available.

What safety factor should I apply to motor sizing calculations?

Apply a safety factor of 10-25% to account for variations in load, voltage fluctuations, and future requirements. Higher safety factors may be needed for critical applications or harsh operating conditions.

How does supply voltage affect motor performance?

Motor torque varies with the square of supply voltage, while current varies inversely with voltage. Lower voltages result in higher currents and potential overheating. Ensure supply voltage matches motor nameplate ratings within ±10%.