Bicycle Gear Inches Calculator

Work out bicycle gear inches instantly with clear inputs, formula shown and shareable results.

About Bicycle Gear Inches Calculator

Gear inches is the ratio times wheel diameter in inches — the equivalent diameter of a direct-drive penny farthing wheel. Development is the distance travelled per pedal revolution, which combined with cadence gives road speed directly.

Formula

Gear inches

gear inches = (chainring / cog) x wheel diameter (in); development = ratio x pi x wheel diameter

Worked example

With the default values below, Bicycle Gear Inches Calculator returns Gear inches of 95.61. Change any input above and every figure here is recalculated in your browser.

Inputs used

Chainring teeth: 50 teeth
Rear cog teeth: 14 teeth
Wheel diameter: 680 mm
Cadence: 90 rpm

Results

Gear inches: 95.61 in
Development per revolution: 7.63 m
Speed at that cadence: 41.20 km/h
Gear ratio: 3.57 :1

Step by step

1Values used
2Gear inches
3Gear inches= 95.61 in
4Development per revolution= 7.63 m
5Speed at that cadence= 41.20 km/h
6Gear ratio= 3.57 :1

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What gear inches are typical?

About 30-40 for a low climbing gear, 70-80 for cruising and 100-120 for a high top gear. Track sprinters use 100-110 fixed.

Why use development instead?

It is metric and intuitive: 7 m per pedal stroke at 90 rpm is 37.8 km/h. Gear inches is a historical convention that survives in English-speaking cycling.