Compare gear changes
See how tooth counts, transmission gears, differential ratios, and tire diameter change RPM, road speed, and ideal torque multiplication.
Free drivetrain calculator
Free Gear Ratio Calculator
A gear ratio calculator compares driving and driven gears to show the change in RPM and ideal torque. Use drivetrain mode to estimate overall ratio, road speed, wheel RPM, and engine RPM at a target speed.
Core formulas
gear ratio = driven teeth / driving teeth
overall ratio = transmission x final drive
Compare two gears
The ratio is driven teeth divided by driving teeth.
Gear ratio
3 : 1
Reduction ratio
- Output RPM
- 1,000
- Ideal output torque
- 300 lb-ft
ratio = driven teeth / driving teeth
output RPM = input RPM / ratio
ideal output torque = input torque x ratio
Use consistent inputs
Use the ratio for the selected transmission gear, the axle final drive, and the actual loaded tire diameter for the closest planning estimate.
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Start a carpoolGear Ratio Calculator FAQ
What is a gear ratio calculator?
A gear ratio calculator compares the driven gear with the driving gear and estimates how the ratio changes rotational speed and torque. For a vehicle, it can combine transmission and final-drive ratios.
How do you calculate gear ratio from teeth?
Divide the number of teeth on the driven gear by the number on the driving gear. A 36-tooth driven gear and 12-tooth driving gear produce a 3:1 reduction.
How do transmission and final-drive ratios combine?
Multiply the selected transmission gear ratio by the differential or final-drive ratio. A 0.75 transmission gear and 3.73 final drive produce a 2.7975:1 overall ratio.
Why can actual vehicle speed differ from the estimate?
Real speed varies with loaded tire radius, tire growth, converter or clutch slip, driveline losses, and measurement tolerances. Treat the result as a planning estimate.