Understanding Gear Motor Torque

In mechanical engineering and industrial design, calculating the torque of a gear motor is critical for ensuring that a system can handle its intended load. Torque represents the rotational force produced by the motor after passing through a gearbox. This Gear Motor Torque Calculator helps you determine the final output force based on the power source and the rotational speed (RPM).

How to Use the Torque Calculator

To use this tool, you need three primary pieces of information: the input power, the output speed, and the efficiency rating. First, select your power unit (Horsepower or Kilowatts). Enter the output RPM—this is the speed at the shaft of the gearbox, not the motor itself. Finally, enter the efficiency of the gearbox; most standard spur gears or helical gears range from 85% to 98% efficiency. Click calculate to see the results in Nm, lb-ft, and kg-cm.

The Torque Calculation Formula

The relationship between torque, power, and speed is defined by physics. For metric units, the formula is:

Torque (Nm) = (Power (kW) × 9550) / Speed (RPM)

When working with imperial units, the constant changes:

Torque (lb-ft) = (Power (HP) × 5252) / Speed (RPM)

Note that when using a gearbox, the efficiency factor (η) must be multiplied by the final result, as mechanical friction and heat dissipation result in a loss of actual output force.

Frequently Asked Questions

Why does torque increase when speed decreases?

Due to the law of conservation of energy, power remains constant (minus efficiency losses). Since Power = Torque × Angular Velocity, if you reduce the speed through gear reduction, the torque must increase proportionally to maintain the power balance.

What is gearbox efficiency?

Gearbox efficiency is the ratio of output power to input power. It accounts for energy lost to heat, vibration, and friction between the gear teeth and bearings. High-precision planetary gears usually have higher efficiency than worm gears.