Bike Gear Calculator

Every gear on a bike is a ratio — chainring teeth over sprocket teeth — multiplied by how far the wheel rolls in one turn. This calculator works out that distance from the wheel and tire you pick, then shows every combination of your chainrings and cassette as a chart in the measure you choose. Change any input and the chart follows; the setup is kept in the page address, so a copied link opens the same bike.

The five measures

Gear inches is the oldest: the diameter of a wheel that, driven directly like a penny-farthing's, would go as far per pedal turn. A 50-tooth ring and an 11-tooth sprocket on a 700 × 28 tire is about 121 inches; 34 × 32 on the same wheel is about 28. Development is the distance in metres the bike travels per crank turn — 9.68 m and 2.26 m for those two gears. Gain ratio, Sheldon Brown's measure, divides the distance the bike moves by the distance your foot moves, so it also counts crank length: 50 × 11 is 8.93 with 172.5 mm cranks and 9.34 with 165 mm. Speed shows how fast each gear goes at the cadence you set — 52.3 km/h in 50 × 11 at 90 rpm — and cadence turns that round, showing the pedalling rate each gear needs to hold a speed: 30 km/h is 70 rpm in 50 × 15 and 104 rpm in 34 × 15.

The steps between gears

Under each figure is the jump from the next larger sprocket, as a percentage: going from 12 teeth to 11 makes the gear 9% harder, and from 32 to 28 makes it 14% harder. Small, even steps keep your cadence steady on a road bike; wide-range mountain cassettes trade them for a lower bottom gear. The step comes from the tooth counts alone, so it is the same in every measure.

Internal-gear hubs

A hub gear such as a Rohloff, a Shimano Alfine or Nexus, or a Sturmey-Archer replaces the cassette: one chainring drives one sprocket, and the hub multiplies that by each of its own ratios. Choose Internal hub, pick the model and type the sprocket. The ratios cannot be worked out from tooth counts, so each one here is copied from the manufacturer's published table. Gears are numbered the way the shifter numbers them, with 1 the lowest, and a 40-tooth ring with a 16-tooth sprocket on a Rohloff is 67 gear inches in its direct-drive eleventh gear.

Wheel size and rollout

Wheels are listed by their ISO bead-seat diameter — the rim measurement the tire actually seats on — with the traditional names beside it, because "26-inch" alone has meant at least three different rims. The calculator assumes the tire is about as tall as it is wide, which comes within about 1% of a measured tire for most road and gravel widths and reads slightly short for very wide mountain tires. For a precise figure, measure your own rollout: mark the tire and the floor, roll the bike one full wheel turn with your weight on it, and measure the distance. A rollout you type in is used exactly as entered.

The cassette presets are a handful of common Shimano and SRAM ranges; type your own sprockets for anything else — any separator works, and the list is sorted for you. Everything is worked out in your browser, and nothing is sent anywhere.

Print a stem sticker prints just the chart, in the measure you are showing, as a small black-and-white strip with the setup on top — cut it out and tape it to your stem or top tube to see which gear you are in.