Gear Ratio Calculator

How to calculate a gear ratio

1. Enter the number of teeth on the driving and driven gears.
2. Enter the input speed and torque.
3. See the ratio and the output speed and torque.

Frequently asked questions

What does the efficiency do?

Real gears lose some power to friction. Spur gears are often about 95 to 98% efficient per stage; 100% gives the ideal output.

How is the gear ratio worked out?

Teeth on the driven gear divided by teeth on the driving gear. 40 / 20 is 2:1, which halves the speed and doubles the torque.

Which way does the output turn?

Two meshing external gears turn in opposite directions. An idler gear between them keeps the direction without changing the ratio.