Bike Gear Inches Calculator
Convert a chainring and cog combination into gear inches and development to compare gearing across any bike.
How it works
Gear inches = (chainring ÷ cog) × wheel diameter (in) · Development = gear inches × π × 0.0254 m
Gear inches expresses any gear as the diameter of an equivalent direct-drive high-wheeler — it multiplies the chainring-to-cog ratio by the driven wheel's diameter, letting you compare gearing across bikes with different wheel sizes. Higher gear inches means a bigger push per pedal stroke (faster but harder); lower means easier spinning for climbs. Development, the metres travelled per crank revolution, is the metric-friendly cousin of the same idea.
Worked example
A 50-tooth chainring with a 17-tooth cog is a 2.94:1 ratio. On a 26.3-inch 700c wheel that is 2.94 × 26.3 ≈ 77.4 gear inches, rolling about 6.18 m per pedal revolution.
Sources: Gear inches (Wikipedia)
Frequently asked questions
What are gear inches?
The diameter, in inches, of the front wheel a penny-farthing would need to travel the same distance per pedal turn as your geared bike. It rolls wheel size and gear ratio into one comparable number.
What is a typical gear-inch range?
Road bikes span roughly 30 gear inches (easiest climbing gear) to 120+ (top-end sprint). Mountain bikes go lower for steep, loose terrain. Under about 20 is a very low bail-out gear.
What is development or roll-out?
The distance the bike travels in one full crank revolution, in metres. It is gear inches converted to metres — many European cyclists prefer it because it maps directly to speed at a given cadence.
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This calculator is for educational purposes. Double-check important results before acting on them.