Gear Ratio Calculator
Calculate gear ratio, output shaft speed, and torque multiplication factor from driver and driven gear tooth counts and input RPM.
Results
What is it?
A gear ratio describes the relationship between the number of teeth on two meshing gears. When the driven gear has more teeth than the driver, the output shaft turns slower (speed reduction) but with proportionally more torque. When the driven has fewer teeth, the output turns faster (overdrive) with less torque. Gear ratios are fundamental to transmissions, gearboxes, and all mechanical power transmission systems.
How to use
Enter the tooth count for the driving (input) gear and the driven (output) gear, plus the input shaft speed in RPM. The calculator computes the gear ratio, output RPM, and torque multiplication factor. For a gear train with multiple stages, multiply the individual stage ratios together.
Example scenario
A 20-tooth driver meshes with a 40-tooth driven gear. Gear ratio = 40/20 = 2:1 (2.000). Input 1,000 RPM → Output 500 RPM. Torque is doubled. If the electric motor produces 10 N·m at 1,000 RPM, the output shaft delivers 20 N·m (before accounting for gear efficiency losses, typically 95–99% per stage).
Pro tip
Compound gear trains multiply ratios. A two-stage gearbox with 3:1 on stage 1 and 4:1 on stage 2 gives 12:1 overall. For very high ratios, consider worm gears (up to 300:1 in a single stage) or planetary/epicyclic arrangements. Backlash (play between gear teeth) becomes critical for precision positioning applications — specify zero-backlash gears or preloaded gear pairs.