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engineering

Gear Ratio Calculator

Find the gear ratio, output speed, torque, and mechanical advantage of a gear pair, in metric or imperial.

Gear ratio
3 : 1
36 driven ÷ 12 driver teeth. A ratio above 1 is a reduction — the output turns slower but with more torque.
Output speed
500 rpm
Output torque
150 N·m
Mechanical advantage
3×

How it works

  1. 1Enter the number of teeth on the driver and driven gears.
  2. 2Add the input speed (rpm) and torque to see the output values.
  3. 3Read the ratio, output speed, output torque, and mechanical advantage.

Use cases

  • Design a gearbox or bicycle drivetrain for a target speed.
  • Work out the torque multiplication of a gear reduction.
  • Check how a gear pair changes rpm between input and output shafts.

Frequently asked questions

How do you calculate gear ratio?

Divide the number of teeth on the driven (output) gear by the teeth on the driver (input) gear. A 36-tooth driven gear with a 12-tooth driver gives a 3 : 1 ratio.

What does a gear ratio above 1 mean?

It is a reduction: the output shaft turns slower than the input but delivers proportionally more torque. A ratio below 1 is an overdrive — faster output, less torque.

How does gear ratio affect torque?

Output torque equals input torque multiplied by the gear ratio (ignoring friction losses), while output speed is the input speed divided by the ratio.

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