Gear Ratio Calculator
Work out gear ratio, output speed and torque multiplication from tooth counts.
Results update as you type.
About this calculator
A gear ratio is the ratio of driven (output) teeth to driving (input) teeth: ratio = driven / driving. A ratio above 1 reduces speed and multiplies torque by the same factor; output RPM = input RPM ÷ ratio and output torque = input torque × ratio.
Frequently asked questions
How is gear ratio calculated?
Divide the number of teeth on the driven gear by the number on the driving gear. A 35-tooth driven gear on a 10-tooth driver is 35 / 10 = 3.5:1.
How does gear ratio affect speed and torque?
A reduction ratio of 3.5:1 turns the output 3.5 times slower than the input but multiplies torque by 3.5, ignoring friction losses.
What is a compound gear ratio?
When two gear pairs are in series, the overall ratio is the product of the two: a 3:1 stage feeding a 2:1 stage gives 6:1 total reduction.
Results are estimates for general guidance only, not financial, medical or tax advice.