Gear ratio calculator
Enter the tooth counts of the driving and driven gears with the input speed and torque to get the ratio, output speed and output torque. Useful for engineering students, maintenance technicians and robot builders.
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How to use it
- Enter driver gear teeth, driven gear teeth, input speed and input torque.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Ratio = driven teeth ÷ driver teeth. Output speed = input speed ÷ ratio. Output torque = input torque × ratio (assuming 100% efficiency).
Example
Inputs: Driver gear teeth = 20, Driven gear teeth = 60, Input speed = 1,500 rpm, Input torque = 10 N·m. Result: Gear ratio: 3 : 1; Output speed: 500 rpm; Output torque: 30 N·m.
Limits and caveats
- Assumes no friction loss, so real output torque is slightly lower.
- Covers one gear pair. For a gear train, multiply the ratios of each pair.
Questions about this tool
What does a 3:1 ratio mean?
The driven gear turns once for every 3 turns of the driver, so speed drops to a third and torque rises about 3 times.
Should I use tooth count or diameter?
For meshing gears of the same module, the tooth ratio equals the pitch diameter ratio, so both give the same answer.
Does an idler gear change the ratio?
No. An idler between two gears only reverses the direction of rotation; the overall ratio stays the same.