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Gear ratio calculator
Compare gearing and speed at your riding cadence.
Drivetrain preset
50T compact road setup.
Gear inputs
50 T
T
17 T
T
90 rpm
rpm
Speed by cadence
70 rpm26.4 km/h
80 rpm30.2 km/h
90 rpm33.9 km/h
100 rpm37.7 km/h
110 rpm41.5 km/h
Terrain range
Fast2.45+
Rolling1.55-2.45
Climb1.05-1.55
Wall<1.05
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About gear ratios
A bicycle gear ratio is the chainring tooth count divided by the rear sprocket tooth count. It describes how many wheel revolutions one crank revolution produces. Wheel circumference determines rollout, and cadence determines calculated speed. A lower ratio gives a lower gear; a higher ratio travels farther per pedal turn.
- How is speed calculated?
- Rollout in metres equals gear ratio multiplied by wheel circumference in metres. Speed in km/h equals rollout multiplied by cadence in rpm and by 60, divided by 1,000.
- Why does tyre size change the result?
- The wheel travels its circumference with each revolution. A different effective tyre circumference changes rollout and speed even when the chainring and rear sprocket stay the same.
- Does a matching ratio mean the parts are compatible?
- No. Ratio calculation does not check freehub type, chain, derailleur capacity, speed count, or manufacturer compatibility. Check those before buying drivetrain parts.