Final Drive Ratio Calculator
Compute the final drive (differential) ratio from ring and pinion teeth, and see the output RPM for any input shaft speed.
Category: Cars & Vehicles
About this tool
What Is Final Drive Ratio Calculator? The Final Drive Ratio Calculator works out the differential (final drive) ratio by dividing the number of teeth on the ring gear by the teeth on the pinion. If you also enter an input speed, it shows the axle output RPM. How It Works The final drive ratio is ring teeth divided by pinion teeth — for example 41 ÷ 11 ≈ 3.727. Multiplying this ratio by the engine output speed at the differential input gives the axle speed; the tool reports output RPM = input RPM ÷ ratio. Worked Example With a 41-tooth ring and 11-tooth pinion the ratio is 3.727:1. A differential input of 3000 RPM yields 3000 ÷ 3.727 ≈ 805 RPM at the axles, which a wheel/tire combination can then convert to road speed. Common Use Cases read the stamped ring/pinion tooth counts on a differential or parts sheet estimate axle speed and, with tire size, approximate road speed for a ratio choose between final drive ratios when planning gear changes Important Notes road speed also depends on tire diameter and transmission gear, not shown here a numerically higher final drive improves acceleration but raises cruising RPM the ring is usually external and the pinion internal; only tooth counts are needed Related Tools Gear Ratio Calculator Tire Size Calculator Speed Converter Car Trip Distance Calculator Frequently Asked Questions What is a typical final drive ratio? Passenger cars commo