Bicycle Gear Calculator
Works out gear ratio, gear inches, development and speed at a cadence for any chainring, sprocket and wheel combination.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
ratio = chainring ÷ sprocket gear inches = ratio × wheel diameter (in) development (m) = ratio × wheel circumference speed = development × cadence × 60
Each pedal revolution turns the wheel by the ratio, and the wheel covers its circumference per turn. Gear inches multiply the ratio by the wheel diameter instead — a leftover from high-wheel bicycles, where the gear was literally the size of the wheel — but it is the convention everyone compares gears in.
What to watch out for
Rough bands in gear inches:
- Under 30 — mountain-bike granny gears and loaded touring.
- 30–50 — climbing.
- 50–80 — most riding.
- 80–110 — fast flat and descending.
- Over 110 — sprint and downhill only.
The useful cadence range is roughly 70–100 rpm. A gear that needs 60 rpm to hold a speed is too high for that speed; one that needs 110 is too low — the range of gears you need is the range of speeds you ride, divided by the cadence you can hold.
Frequently Asked Questions
How do I calculate bicycle gear inches?
Chainring teeth ÷ sprocket teeth × wheel diameter in inches. 50/17 on a 700c road wheel (about 26.4 in with a 25 mm tyre) is 2.94 × 26.4 = 77.6 gear inches.
What is development on a bicycle?
How far the bike travels per pedal revolution — the ratio times the wheel circumference. 50/17 on a 2,105 mm wheel is 6.19 m per stroke, so at 90 rpm that is 33.4 km/h.
Why compare gears in inches rather than teeth?
Because the wheel size changes the gear. A 50/17 on a 20-inch folding bike is about 59 gear inches; the same teeth on a 29er is 86. Gear inches and development put every bike on one scale.