What is it?
The Gear Ratio Calculator works out how two gears change speed and turning force. It shows the gear ratio, output speed, output torque and whether the gears slow things down or speed them up.
Who is it for?
Mechanics, cyclists, machine and motor users, and engineering students.
How to use it
Enter the Teeth on the driving gear and the Teeth on the driven gear, plus the Input speed (rpm), Input torque and Efficiency. The answer appears as you type; there is no Calculate button. Tap Copy result to copy it, or Share on WhatsApp to send it.
How it works
Ratio = driven teeth ÷ driving teeth. The same works for pulleys (use diameters) and bicycle sprockets.
- Ratio above 1 (reduction): the output turns slower with more torque. A 10-tooth gear driving a 40-tooth gear: 4:1, a quarter of the speed, about four times the torque.
- Ratio below 1 (overdrive): faster, less torque.
Examples
- Pulley: a 1,440 rpm motor with a 4-inch pulley driving a 12-inch pulley turns the machine at 480 rpm.
- Bicycle: a 44-tooth front chainring and 11-tooth rear sprocket is 0.25: the wheel turns 4 times per pedal turn.
Efficiency covers friction losses: about 95–98% per stage for good gears, less for belts and worm gears.
Worked example
A 12-tooth gear driving a 36-tooth gear: ratio 3:1; 1,500 rpm in gives 500 rpm out with about three times the torque.
Errors and how to fix them
- “Enter the driving teeth / the driven teeth (more than 0)”
Open the tool: Gear Ratio Calculator
Still stuck?
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Questions, or an error not listed here?
Tell us in the comments: what you were doing, the exact message you saw, and your device and browser. We read every comment and add new fixes to this article.