Bike Gear Ratio and Gear Inches Calculator
Gear inches, development, ratio and speed at any cadence for every gear on your bike — with the overlapping gears you cannot actually feel flagged.
| Gear | Ratio | Gear inches | Development | Gain | Speed |
|---|
Reading the table
- Gear inches is the diameter a direct-drive wheel would need to go as far per pedal stroke. It collapses ring, sprocket and wheel size into one number you can compare across bikes.
- Range is the spread from easiest to hardest, and it is what cassettes are marketed on. A 510% range means the hardest gear is just over five times the easiest.
- Rows flagged as duplicates sit within 3% of the gear above — a step too small to feel. On a double chainset several usually do, which is the practical argument for a single ring.
- Gain ratio accounts for crank length, which gear inches cannot. A longer crank makes the same gear easier, and only this column shows it.
How to use
- Enter your chainrings and cassette, or start from one of the presets.
- Pick your wheel and tyre so the speeds are right.
- Set the cadence you actually ride at, not the one you aspire to.
- Read the range, and check which gears are flagged as duplicates.
Frequently asked questions
What is a gear inch?
The diameter a direct-drive wheel would need to travel as far per pedal stroke as your gear does — a leftover from penny-farthings that survived because it works. It collapses chainring, sprocket and wheel size into one number, which is what lets you compare a mountain bike gear with a road one without doing the arithmetic each time.
What is the difference between gear inches and development?
Units, and nothing else. Development is metres travelled per crank revolution, which is the metric way of saying the same thing. Both are shown because riders think in whichever they grew up with, and converting between them is a fixed multiplication.
Why does the table flag some gears as duplicates?
Because a step you cannot feel is not a step. Gears within about 3 per cent of the one above are effectively the same gear reached two ways, and on a double chainset with a close cassette there are usually several. It is the clearest argument for a single chainring: fewer nominal gears, but more that are actually distinct.
What does gear range mean when a cassette is sold on it?
The spread between the easiest and hardest gear as a percentage. A 10-51 cassette is 510 per cent, meaning the hardest gear is just over five times the easiest. It tells you what the drivetrain can cover, and says nothing about how evenly it is spaced — a wide range with big jumps can be harder to ride than a narrow one.
What is gain ratio and why is it not the same as gear inches?
Gain ratio accounts for crank length, which gear inches cannot. A longer crank gives more leverage, so the same gear is genuinely easier to turn — Sheldon Brown argued for gain ratio precisely because two riders on identical gearing with different cranks are not riding the same gear. Change the crank length here and only that column moves.
Does the wheel and tyre choice really matter?
For gear inches, a little; for speed, a great deal. A 29 inch mountain wheel rolls noticeably further per revolution than a 700x25, so the same ratio gives a different speed. Picking the wrong one here does not change which gears overlap, but it will give you speeds that are several km/h out.
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