Gear Ratio Calculator

Enter the teeth on the driving and driven gears and the input speed.

This result is an estimate only. Double-check important figures before relying on them.

How it is calculated

Gear ratio = driven teeth ÷ driver teeth
Output speed = input speed ÷ ratio
Ideal torque = input torque × ratio

For the turning effect itself, use the torque calculator.

Worked example

A 20-tooth gear driving a 60-tooth gear at 1,500 rpm:

Ratio = 60 ÷ 20 = 3:1
Output = 1,500 ÷ 3 = 500 rpm, with three times the torque

Why your number may differ

Real gear trains lose a few percent to friction, and belts or chains can slip. Use the same method for belt pulleys by counting diameters instead of teeth.

Frequently asked questions

How is the gear ratio calculated?

Divide the teeth on the driven gear by the teeth on the driving gear. A ratio of 3 means the output turns three times slower with three times the torque.

What does a ratio below 1 mean?

The output turns faster than the input, with less torque. This is an overdrive.

Is torque exactly multiplied?

Only ideally. Friction losses mean the real output torque is a little lower.