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Sports & Performance

Bicycle Gear Calculator

Calculate bicycle gear ratio, gear inches, development, and cadence-based speed from tooth counts and a measured loaded wheel rollout.

Published

Gear ratio
Gear ratio
2.50:1
Gear inches
65.79 in
Development
5.25 m/rev
Speed
17.6 mph
Speed
28.35 km/h

Theoretical no-slip rollout from your measured loaded wheel value. Tire slip, dynamic deformation, drivetrain loss, wind, grade, acceleration, and rider power are not modeled.

Wheel measurement
Accepted range: 100–10000 mm (0.1–10 m after conversion).
mm
rpm

Results update as you type.

Bicycle Gear Calculator

Calculate external gear ratio, gear inches, development, and theoretical speed from chainring and rear-cog tooth counts, cadence, and measured loaded wheel geometry.

For the former compact workflows, use the gear-ratio preset or cadence preset.

Measure the wheel rollout

Inflate the tyre to normal riding pressure. Mark the tyre and ground at the valve, load the bicycle as it is ridden, roll straight for one complete wheel revolution, and measure between the marks. Enter that rollout as circumference.

Use diameter mode only for a directly measured loaded outside/effective diameter. Do not enter a nominal wheel-family label.

Method

For this direct external drivetrain, the gear ratio is chainring teeth divided by rear-cog teeth. Development is measured circumference multiplied by that ratio. Effective diameter is circumference divided by π, and gear inches is that diameter in inches multiplied by the ratio. Theoretical speed is development multiplied by cadence and converted from metres per minute to km/h and mph.

Calculations keep full precision until the displayed result. Enter valid numbers within the shown ranges. The calculator does not show a result when a value is missing, outside its range, or would make the calculation undefined.

Limits

The result is theoretical no-slip rollout. Tire slip, dynamic deformation, drivetrain loss, wind, grade, acceleration, and rider power are not modeled. It does not prescribe gearing, cadence, training, safety, or performance.

Sources

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Bicycle Gear Calculator updated at