Bike Gear Ratio Calculator

How to read your results

Every gear is one chainring paired with one cog. The calculator shows five ways to describe the same gear. They all grow in step with the gear ratio, so pick the one you think in. The worked example is a 50-tooth chainring and an 11-tooth cog on a 700x28c tyre (28-622, 2,136 mm rollout), with 172.5 mm cranks at 90 rpm.

Gear inches are the diameter of a penny-farthing wheel that would feel the same. They are the standard unit in the US and in Sheldon Brown's tables. Development is the same idea in metres travelled, which is how most European riders compare gears. Gain ratio, Sheldon Brown's measure, also counts the crank: the bike moves 9 times as far as your pedal does. Longer cranks lower it, so it is the fairest way to compare bikes with different crank lengths.

Typical gearing by discipline

Presets from the calculator, on 700x28c unless noted.

As a rule of thumb, gears under 30 gear inches (about 2.4 m) get a loaded or unfit rider up 10% grades, 65–85 inches is everyday cruising, and anything over 110 inches is for descents and sprints. Urban fixed-gear riders usually pick 65–75 inches, track riders 85–95.

1x or 2x?

A 1x drivetrain gives up gears, not range. The Rival XPLR setup above has 12 gears over 440%, so the average step between gears is about 14.5%. The GRX double covers 507% with 20 usable gears and 9% steps. On a 1x you feel every shift, and on the flat you often sit between two gears. A 2x keeps cadence steady but needs a front shift and has near-duplicate gears: on 50/34 × 11-34, the 34×13 and 50×19 differ by less than 1%. The calculator marks such pairs with a dashed ring.

Cross-chaining

On a double, the big ring with the biggest cogs and the small ring with the smallest cogs run the chain at a steep angle. That is noisier, wears the chain and cogs faster and loses a little efficiency. The calculator works out the angle from the chainstay length and cog spacing. It flags gears over 2.7° on a double, for example 50×30, 50×34, 34×11 and 34×12 on a 12-speed compact. On a triple it flags the three most crossed cogs on the small and big ring. A 1x chainline is centred on the cassette, so no gear is flagged there.

Why tyre size matters

Wheel size changes every number except the ratio. Tyres are listed by their ETRTO size, for example 28-622 (28 mm wide on a 622 mm rim). The outside circumference is about π × (rim diameter + 2 × tyre width): 2,105 mm for a 700x25c and 2,200 mm for a 700x40c. So the same 50×11 rolls 4.5% further on the gravel tyre. If you know your measured rollout, type it into the circumference field.