Bike Size Calculator

Use this calculator to get a starting frame size from inseam. Enter inseam in centimetres (cm) or inches (in); the unit selector converts the value to centimetres before the calculation.

Road frame size (cm) ≈ 0.65 × inseam in centimetres. Mountain-bike size (in) ≈ 0.226 × inseam in centimetres. An 82 cm inseam suggests about 53 cm road and 18.5 in mountain. Measure inseam in cycling socks with a book pressed up between the legs.

Modern brands size bikes by virtual top-tube, stack, and reach as much as by seat-tube length. Treat this as a starting aisle in the shop, not a bike fit. Standover, reach, and stem length still need checking on the actual bike.

Inseam: Inside-leg length, book pressed up. Enter cm or in.

Road: Suggested road frame size in centimetres (classic centre-to-top seat-tube convention).

MTB: Suggested mountain-bike size in inches.