Work out a gear ratio from driver and driven teeth, with output speed and torque — plus multi-stage ratios in Advanced.
How to use this tool
Enter the driver gear's teeth (the gear doing the driving) and the driven gear's teeth.
Type the driver gear's RPM to get the output RPM. Leave it blank if you only need the ratio.
A ratio above 1 slows the output down and multiplies torque by the same factor; a ratio below 1 (overdrive) speeds it up and reduces torque.
For gearboxes with two reductions, enter the second pair too: the total ratio is the two ratios multiplied together.
Formula & worked example
A 20-tooth driver turning a 60-tooth gear gives 60 ÷ 20 = 3:1. At 3,000 RPM input the output turns at 1,000 RPM and ideal torque is multiplied by 3.
Limitations — read this before you rely on it
Tooth counts must be whole numbers, and the torque figure is ideal — real gearboxes lose roughly 2–5% per gear mesh to friction, and very high ratios may need several stages in practice. This calculator treats the gears as a simple pair; it does not check whether the gears physically mesh (module, pressure angle and centre distance all matter in a real design).
Frequently asked questions
The driver turns 3 times for every 1 turn of the driven gear. Output speed is a third of input speed, and output torque is (ideally) three times the input torque.
The gear that receives power first — usually the one on the motor or engine shaft. Swapping driver and driven inverts the ratio.
Gears trade speed for torque: the same power at a lower speed means more torque, and vice versa. Power is conserved (minus friction losses); it is never created by gearing.
Multiply the stages: a 3:1 first stage followed by a 2:1 second stage gives 6:1 overall. That is how gearboxes reach large reductions without one enormous gear.
A ratio below 1:1, where the output turns faster than the input — used for cruising, where you want speed rather than torque. Torque drops by the same factor.