Calculate gear ratio, output speed and torque from gear teeth.
Calculated instantly in your browser.
How do you calculate gear ratio?
Gear ratio = driven teeth ÷ driving teeth. Output speed = input rpm ÷ ratio, and output torque ≈ input torque × ratio. A ratio above 1:1 is a reduction (slower, more torque). For example, a 12-tooth driving gear with a 36-tooth driven gear gives a 3:1 reduction — 3,000 rpm in turns 1,000 rpm out with three times the torque.
Understanding your result
A ratio above 1:1 is a reduction: the output turns slower but with more torque. Below 1:1 is an overdrive: faster output, less torque. The simplified ratio expresses the same relationship in the smallest whole numbers.
Formula and method
Gear ratio = driven teeth ÷ driving teeth. Output speed = input rpm ÷ ratio. Output torque ≈ input torque × ratio (ignoring losses).
Worked example
A 12-tooth driving gear with a 36-tooth driven gear gives a 3:1 reduction — at 3,000 rpm in, the output turns 1,000 rpm with three times the torque.
How to use this tool
- Enter the driving gear’s tooth count.
- Enter the driven gear’s tooth count.
- Optionally add input rpm to get output speed.
Common mistakes to avoid
- Swapping the driving and driven gears.
- Ignoring friction and efficiency losses in real drivetrains.
About the Gear Ratio Calculator
The Gear Ratio Calculator works out the ratio between two gears from their tooth counts, then gives the simplified ratio, the output speed for a given input rpm and the torque multiplier.
Who should use this tool
Mechanics, cyclists, RC and robotics builders, and anyone designing a drivetrain.
Benefits
- Gear ratio as a decimal and a simplified whole-number ratio.
- Output rpm from any input speed.
- Torque multiplier for the gear pair.
- Explains reduction vs overdrive.
Practical use cases
- Choosing sprockets for a bike or motorcycle.
- Designing a robot or RC gearbox.
- Checking a final-drive ratio.
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Frequently asked questions
What does a 3:1 gear ratio mean?
The driving gear turns three times for every one turn of the driven gear, producing three times the torque at one-third the speed.
Does a higher ratio mean more speed?
No — a higher ratio (reduction) means more torque and lower output speed. A lower ratio (overdrive) gives more speed and less torque.