Gear Ratio Calculator
Gears trade speed for turning force. A small gear driving a large one slows the output and gives it more force. This page works out the ratio from the teeth on two meshing gears, and the speed that results.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
The gear ratio is the number of teeth on the driven gear divided by the number on the driver. The driven gear turns at the driver's speed divided by that ratio.
This assumes ideal meshing gears with no slip or friction. Chains, belts and multi-stage trains follow the same logic: multiply the ratios of each stage.
Worked example
A driver gear with 20 teeth meshing with a 60 tooth gear has a ratio of 3. At 1,800 rpm, the driven gear turns at about 600 rpm.
Questions
What does a ratio above 1 mean?
It means the driven gear is bigger, so it turns slower and with more turning force than the driver.
Do the two gears turn the same way?
Two meshing gears turn in opposite directions. An idler gear placed between them makes both turn the same way.
Does this include losses?
No. Friction and wear reduce the real output a little, so the figure is the ideal case.
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