Gear ratio and development calculator.

How it works

The ratio is the chainring's teeth divided by the sprocket's teeth: with 50 and 25 teeth, the rear wheel turns twice for each turn of the cranks. Development multiplies the ratio by the wheel's circumference, so it is the distance the bike moves for one crank turn. Gear inches multiply the ratio by the wheel's diameter in inches.

Wikipedia says the ISO 5775 system labels tyres by the tyre's width and the rim's bead seat diameter in millimetres, for example 28-622; BSI lists BS ISO 5775-1:2023, the standard for tyre designations, as current. Wikipedia's conversion table matches 622 mm to the names 700C and 28-inch, 584 mm to 650B or 27.5-inch, 559 mm to 26-inch and 630 mm to 27-inch.

Without a measured roll-out, the calculator estimates the wheel's circumference as pi times the bead seat diameter plus twice the tyre width. That is arithmetic on the label, not a measurement; the calculator also accepts a measured roll-out in its place.

The UCI's gear test, for comparison

The UCI announced a test of a maximum gear of 54 x 11, which it described as 10.46 metres per crank revolution. With a 28-622 tyre, this calculator's estimate also gives 10.46 m for 54 x 11. At its 2 to 4 June 2026 meeting the UCI said the test protocol remains suspended after the Brussels Court of Appeal dismissed its appeal against the Belgian Competition Authority's decision of 9 October 2025, and that it will appeal to the Belgian Court of Cassation. No UCI gear limit is in force. A race's own rules and its officials have the final word on any equipment question.