CalculatorsBike Frame Size Calculator

Bike Frame Size Calculator

Frame size is an inseam problem first. Road multiplies inseam by 0.665, gravel by 0.655, MTB by 0.64, then nudges a centimetre if your torso is unusually long or short for that inseam.

Inputs

Inseam (in)Barefoot, book between the legs, measure to the floor.Height (in)Discipline

Results

Frame size: 21.9 in
Frame size: 21.9 in

How the number is made

Frame centimetres = inseam × discipline factor. If height ÷ inseam is under 1.95 the result drops 1 cm (long legs, shorter torso). Over 2.15 it rises 1 cm. Inches are that centimetre size ÷ 2.54.

The factors 0.665 (road), 0.655 (gravel) and 0.64 (MTB) are fitting heuristics, not a brand chart. Height adds or subtracts 1 cm only when height ÷ inseam is outside 1.95–2.15. Standover, stack and reach still choose the frame.

What to do with the number

Treat the result as the size to test, then compare stack and reach on the geometry chart. A 54 cm endurance bike and a 54 cm race bike are not the same cockpit.

Related calculators

Stack and Reach Ratio Calculator
The centimetre size still hides how aggressive the cockpit is.
Optimal Saddle Height Calculator
Inseam sets the saddle before it sets the frame.
Bicycle Gear Ratio Calculator
A smaller frame does not change the gear inches, the chainrings do.

Questions

Is inseam or height the size?

Inseam. Height only shifts the result by a centimetre when your proportions are far from average.

Why is gravel smaller than road?

Gravel frames often run a lower standover for the same reach. The 0.655 factor leaves a little more clearance.

Does this replace stack and reach?

No. Two 56 cm frames can differ by 15 mm of reach. Check the stack/reach calculator next.

Related gear

Tailor measuring tape
Inseam measured against a wall beats a guessed EU size.
$8–$20
Adjustable fit bike session
Use the centimetre result to book a fit, then lock stack and reach.
$150–$400

Disclaimer — no professional advice, no liability

These calculators are simplified estimates for education. They are not a bike fit, a structural inspection, or a torque specification that overrides the number printed on a part. Confirm chain length, spoke length, tire fit and bolt torque on the bicycle before you ride.

These calculators, pages and any related content are provided “as is” and “as available”, solely for general educational and informational purposes. They are simplified mathematical estimates, not a professional bike fit, a structural inspection, a manufacturer torque specification or a training, nutrition or medical plan.

Results can be wrong, incomplete or inapplicable to your frame, wheels, tires, drivetrain or suspension. You must independently verify every figure, assume all risk, and confirm chain length before you cut, spoke length before you lace, tire and rim compatibility before you inflate, and the torque printed on the part before you tighten it.

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