Gear Ratio Speed & Torque Calculator
From input teeth, output teeth and input speed and torque, get the gear ratio, output speed and output torque.
How it works
Ratio = driven ÷ driver · Output rpm = input rpm ÷ ratio · Output torque = input torque × ratio
The gear ratio is the driven tooth count divided by the driver tooth count. A ratio above 1 is a reduction: the output turns more slowly but with proportionally more torque, because power (speed × torque) is conserved in an ideal gearset. Real gears lose a few percent to friction, so treat the output torque as an ideal upper bound.
Worked example
A 12-tooth driver turning a 36-tooth gear gives a ratio of 36 ÷ 12 = 3:1. At 3,000 rpm input the output runs at 3,000 ÷ 3 = 1,000 rpm, and 20 N·m of input torque becomes 20 × 3 = 60 N·m.
Sources: Gear train — Wikipedia
Frequently asked questions
Does a gear reduction increase power?
No. In an ideal gearset power is conserved, so what you gain in torque you lose in speed. A 3:1 reduction triples torque but cuts speed to a third; the product stays the same.
What does a 3:1 gear ratio mean?
The input shaft turns three times for each turn of the output shaft. The output spins one-third as fast and delivers three times the torque (minus friction losses).
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This calculator is for educational purposes. Double-check important results before acting on them.