Gear Train Reduction Calculator

About this calculator

In a simple gear train, the gear ratio is the number of teeth on the driven gear divided by the number of teeth on the driver gear. A larger driven gear turns more slowly than the driver but with proportionally more torque, since (ignoring friction losses) power is conserved: output RPM = input RPM ÷ gear ratio, while output torque = input torque × gear ratio.

This trade-off between speed and torque is the entire point of gearing down — a small motor spinning fast can drive a heavy load slowly but with much greater force, which is why reduction gear trains show up in everything from car transmissions and robotics actuators to power tools and wind turbine nacelles. This calculator takes the driver and driven tooth counts along with the input speed and returns the gear ratio, output RPM, and torque multiplication for the train.