Bike gearing calculator
Estimate speed from bike cadence and gearing
Enter the front chainring teeth, rear cog teeth, pedaling cadence, and the measured wheel rollout circumference in meters. The result assumes continuous pedaling without gear changes or wheel slip.
2.1 m is an example, not a universal road-bike circumference. Measure your inflated tire's actual rollout for a more useful estimate.
The calculation
The gear ratio is front teeth ÷ rear teeth. Each crank revolution turns the rear wheel that many times, assuming a conventional chain drive.
Speed (km/h) = cadence (rpm) × (front ÷ rear) × wheel circumference (m) × 60 ÷ 1000.
Example: 50/17 gearing at 90 rpm
With a 50-tooth chainring, 17-tooth rear cog, and 2.10 m wheel rollout, the ratio is about 2.94. Each crank turn moves the bike roughly 6.18 m. At 90 rpm the theoretical speed is 33.35 km/h (20.72 mph).
Does the calculated speed match outdoor riding?
Not necessarily. It assumes the chosen gear and cadence can be maintained. Wind, hills, tire size, aerodynamic drag, resistance, and coasting all matter. For actual average speed from a ride, use the cycling speed calculator.