Bike Gear Ratio Calculator: Gear Ratio, Gear Inches and Speed

Which gear makes you how fast? This bicycle gear ratio calculator shows your speed, gear ratio and gear inches for every chainring-and-cog combination at a given cadence — sorted from the easiest to the hardest gear. Pick a complete groupset, or set chainrings, cassette, cadence and tire size freely.

Instead of a dry table you get a bar chart: each bar is a gear, its height the speed. Tap a bar to see it as a drivetrain below.

How to calculate bicycle gear ratio, gear inches and development

The gear ratio is the number of chainring teeth (front) divided by cog teeth (rear). 50 up front and 25 in the rear give a ratio of 2.0: one crank revolution turns your rear wheel twice.

Development (or rollout) is how many meters you travel per crank revolution — ratio times wheel circumference. That is exactly why the calculator needs your tire size: a bigger tire rolls farther per revolution, so you go slightly faster in the same gear.

Gear inches are the traditional unit in the UK and the US: the gear ratio multiplied by the wheel diameter in inches. A road wheel with a 700×28C tire has a diameter of about 26.8 inches, so a 50×25 gear (ratio 2.0) is about 54 gear inches. The calculator works this out for you when you tap a bar.

Gear ratio chart: common road bike gears

The chart shows typical road gears with a 700×28C tire (2,136 mm circumference) at a cadence of 90 rpm. For your own setup, use the calculator above.

Theoretical values at a constant cadence, without drivetrain losses. Even the hardest gear gives over 50 km/h at 90 rpm, so most riders need their biggest gear less often than they think — what usually matters is the easiest gear on climbs.

Which gear ratio for a road bike?

Three chainring combinations are common on road bikes: 50/34 (compact), 52/36 (semi-compact) and 53/39 (standard), plus SRAM’s smaller steps such as 48/35 or 46/33. Which one suits you depends less on your top speed than on whether you can still turn the pedals at a sensible cadence on the steepest climb of your usual rides.

A practical rule of thumb: if you regularly drop below 70 rpm on long climbs, your easiest gear is too hard. Compare two setups in the calculator and enter gradient and weight to see the difference. How hard a gear feels ultimately depends on your power — the FTP calculator helps you get started, and the bike pacing calculator shows what power you can hold over a given course.

1x or 2x — which gearing suits you

A 2x drivetrain (two chainrings) gives fine steps and a wide overall range — ideal for road and hilly routes. A 1x drivetrain is simpler, lighter and lower-maintenance: one chainring, but a wider cassette. It is now standard on gravel (SRAM XPLR, Shimano GRX) and MTB (SRAM Eagle, Shimano XT). What matters is not the number of chainrings, but the largest ratio you can reach.

Wheel circumference — where the values come from

The tire presets use the standard circumference table that bike computers from Garmin, Wahoo or Sigma also use — sorted by tire size (700×28C, 27.5″, 29″ …), not by model. Between two tires of the same width the circumference differs by only a few millimeters, negligible for speed. If you want it exact, measure your roll-out circumference once and enter it in the wheel circumference field.