Gear Ratio Calculator

Driven and driver teeth, output RPM, and torque.

A gear ratio is the driven gear's teeth divided by the driver gear's teeth. Enter both tooth counts, plus an optional input speed and torque, to see the output RPM and torque.

Need to simplify a mathematical ratio instead? Try our Ratio Calculator.

Calculator Inputs

Driven Gear Teeth*

Output gear

Driver Gear Teeth*

Input/Motor gear

Input Speed (RPM)

Input Torque (Nm)

Results

Enter values above to see your results

How It Works

Ratio = Driven Teeth / Driver Teeth. Output Speed = Input Speed / Ratio. Output Torque = Input Torque × Ratio.

Driving and driven gears

The driver is the input gear, the one turned by the motor. The driven gear is the output. This calculator uses driven teeth divided by driver teeth.

With 40 teeth on the driven gear and 10 on the driver, the ratio is 40 / 10 = 4, shown as 4:1.

Gear reduction and speed increase

A ratio above 1:1 is a reduction. The output turns slower than the input, and the torque is multiplied by that same ratio.

A ratio below 1:1 is a speed increase. Ten driven teeth and 20 driver teeth is 0.5:1: the output turns twice as fast, and the torque is halved. A 1:1 pair is direct drive.

Input and output RPM and torque

Output speed = input RPM / ratio. Output torque = input torque × ratio. The form's defaults are 1,000 RPM and 5 N·m, so a 4:1 pair gives 250 RPM and 20 N·m.

Those outputs ignore friction. A real gearbox delivers less torque than this ideal multiplication.