Gear Ratio Calculator
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Ratio = driven ÷ driver teeth; output RPM = input RPM ÷ ratio.
Gear pair
Gear ratio
4 : 1
Output: 300 RPM
- Output RPM
- 300
Related calculators
Gear ratios
Gear ratio compares the size of two meshing gears: ratio = driven teeth ÷ driver teeth. A 40-tooth gear driven by a 10-tooth pinion gives ratio 4:1 — the larger gear turns once for every four pinion revolutions, multiplying torque and reducing speed.
Output speed = input speed ÷ gear ratio (for a single stage). Multi-stage gearboxes multiply ratios across stages. Efficiency losses from friction are not modeled here.
Example: 1200 RPM input with a 3:1 reduction yields 400 RPM at the output shaft. Reverse the tooth counts to speed up instead of slow down.
Common questions
Which gear is driver vs driven?
The driver (pinion) is the gear receiving input power; the driven gear is connected to the output. Enter driver teeth in the first field.
Does this include belt or chain drives?
Use pitch diameters or sprocket tooth counts the same way — ratio = output teeth ÷ input teeth for simple drives.