Gear Ratio Calculator
Find the ratio between two gears from their tooth counts, then read the inverse ratio and the speed multiplication for a gear set.
Category: Cars & Vehicles
About this tool
What Is Gear Ratio Calculator? The Gear Ratio Calculator computes the ratio of a gear pair from the number of teeth on the driven gear versus the driving (input) gear. The result is expressed as a classic "Z:1" reduction plus the inverse speed ratio. How It Works Gear ratio equals the number of teeth on the driven gear divided by the number of teeth on the driving gear. A driven gear with more teeth than the driving gear reduces output speed and multiplies torque; the inverse ratio tells you how many times the driven gear turns for each turn of the driving gear. Worked Example A transmission cluster with a 73-tooth driven gear and a 21-tooth driving gear gives about 3.476:1. That means roughly 3.48 turns of the input produce one turn of the output, with torque multiplied by the same 3.476 factor. Common Use Cases read a gear ratio from a graphic or parts list so you can compare drivetrains understand whether a gear set is a reduction or an overdrive back into torue/speed trade-offs when planning a ratio change Important Notes only the tooth count matters here; center distance and pitch diameter are not computed a ratio above 1 is a reduction, below 1 is an overdrive (overdriven output) for a multi-gear sequence multiply the individual pair ratios together Related Tools Final Drive Ratio Calculator Speed Converter Tire Size Calculator horsepower-calculator Car Trip Distance Calc