Gear ratio speed calculator
Calculate road speed from engine RPM and gearing, or engine RPM from road speed.
Use positive transmission and final-drive ratios up to 100, circumference from 100 to 10000 mm, engine-speed input from 0 to 100000 RPM and speed input from 0 to 2000 in the selected unit. Decimal inputs allow up to six places. These are software bounds, not vehicle capability claims. Results use floating-point arithmetic. Processing stays on your device, with a bounded worker and a 10-second timeout. Full JSON and CSV preserve every calculated row and the assumptions. Do not use thousands separators. Up to 1,000,000 characters. Review the settings before running.
Your result
How to use Gear ratio speed calculator
- Choose whether to calculate road speed or engine RPM.
- Enter the transmission and final-drive reduction ratios and rolling tire circumference.
- Enter the selected speed input, calculate and download the full report.
Useful next steps
Follow the complete reduction
Overall reduction is transmission ratio multiplied by final-drive ratio. Wheel RPM is engine RPM divided by overall reduction. Multiplying wheel RPM by rolling circumference and dividing by 60 gives road speed in meters per second.
Calculate in either direction
For engine RPM from road speed, reverse the same formula. Use reduction ratios as input, rather than their reciprocals. The model assumes a locked drivetrain and does not simulate torque-converter slip, clutch slip, tire slip, engine power or road resistance.