Bike Gear Inches Calculator
Enter your chainring teeth, cog teeth and wheel diameter to get three linked numbers: the drivetrain ratio, gear inches, and metres of development per pedal turn. Gear inches reduce any chainring, cog and wheel combination to one figure, so a road bike, a fixie and a mountain bike can be lined up and compared. The maths runs instantly in your browser as you type.
How to calculate gear inches
- Type the chainring (front) tooth count into the 'Chainring teeth' box.
- Type the cog (rear) tooth count into the 'Cog teeth' box.
- Set 'Wheel diameter' in inches; 27 is a good default for a 700c road wheel.
- Read the three result cards: gear ratio, gear inches and development in metres.
- Click Copy to grab the full line of numbers, then change any value to compare another gear.
Examples
Common road gear, 50x15 on a 700c wheel
chainring 50T, cog 15T, wheel 27 in
Ratio 3.33, 90.0 gear inches, 7.18 m development
Compact climbing gear, 34x28
chainring 34T, cog 28T, wheel 27 in
Ratio 1.21, 32.8 gear inches, 2.62 m development
Single-speed 48x17
chainring 48T, cog 17T, wheel 27 in
Ratio 2.82, 76.2 gear inches, 6.08 m development
Frequently asked questions
What are gear inches?
Gear inches express how far a bike rolls for one pedal turn, scaled to the diameter of an equivalent direct-drive wheel from the penny-farthing era. You get them by multiplying the gear ratio (chainring teeth divided by cog teeth) by the wheel diameter in inches. A higher number is a taller, harder gear.
What is metres of development?
Development is the distance the bike actually travels for one full crank revolution. This tool computes it as gear inches times pi, then converts inches to metres, so 90 gear inches works out to about 7.18 metres per pedal stroke.
What wheel diameter should I enter?
Use the rolling diameter of the mounted tire, measured in inches. A 700c road wheel is close to 27 inches, which is the default here. A 26 inch mountain wheel is smaller, and a 650b or a fat tire will differ, so measure if you want precise figures.
How do gear inches help compare bikes?
Because they fold chainring, cog and wheel size into one value, gear inches let you compare setups that otherwise look nothing alike. A track bike with a big wheel and a mountain bike with a small wheel can be judged on equal footing by the single number.
Higher or lower gear inches for climbing?
Lower. A smaller gear-inch number turns the pedals more easily for each bit of forward motion, which suits steep climbs and spinning a high cadence. Higher gear inches push more distance per turn and suit flat sprints and fast descents.
Does this account for crank length or cadence?
No. Gear inches and development describe the drivetrain and wheel only. Crank length changes the leverage you feel but not these numbers, and your speed depends on cadence, which you multiply in separately.
Can I enter values other than whole teeth?
The boxes accept any positive number, so you can try a decimal wheel diameter like 26.4. Real chainrings and cogs have whole tooth counts, but the calculator will still compute a ratio from whatever you type.
Why do I see an error message?
The calculator needs all three boxes filled with positive numbers. Leaving one blank shows 'Enter chainring, cog and wheel diameter', and a zero or negative entry shows 'All values must be positive numbers'.
Is my data sent to a server?
No. The calculation runs entirely in your browser, so nothing you enter is uploaded. You can use it offline once the page has loaded.
Learn more
- Gear inches vs gain ratio and development
Three ways cyclists measure a gear: gear inches, metres of development and gain ratio. What each one means and when to reach for it.
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