How do I measure my inseam?

Stand barefoot against a wall with feet 15 cm apart. Place a hardback book between your legs, spine up, pressed against the wall. Measure from the floor to the top of the book spine.

Is frame size the only thing that matters?

No. Frame size is a starting point. Stack, reach, top tube length and seat tube angle all affect fit. A professional bike fit is recommended for optimal comfort and performance.

What if I am between sizes?

For racing, go smaller (more aggressive position). For comfort and touring, go larger. Many modern bikes come in S/M/L rather than centimetre sizes.

Does the formula differ by bike type?

Yes. Road bikes use inseam (cm) × 0.665 to give a frame size in centimetres. Gravel uses × 0.645 and touring × 0.66. Mountain bikes are sized in inches, so we use inseam (cm) × 0.226 — for an 84 cm inseam that is about 19 inches, roughly equivalent to a road frame minus 11 cm.

What do the estimated stack and reach figures mean?

Stack and reach describe the frame front-end. Stack is the vertical distance from the bottom bracket to the top of the head tube; reach is the horizontal distance. Our stack figure is a first-order estimate (frame size in cm × 10, so a 56 cm frame ≈ 560 mm) and the reach figure is a rough rider target from your torso and arm proportions. Treat both as a starting point and always check against the manufacturer geometry chart.

Frame Size Calculator — Find Your Bike Size

How We Calculate This

Frame Size Calculation

Frame Size (cm) = Inseam (cm) × Bike Type Factor (Cyrille Guimard / Greg LeMond method)

Road bike: × 0.665 → frame in cm
Gravel bike: × 0.645 → frame in cm
Touring bike: × 0.66 → frame in cm
Mountain bike: × 0.226 → frame in inches (MTBs are sized in inches, ≈ road frame − 11 cm)

The standover height is the inseam minus a clearance margin (2 cm for road, 8 cm for mountain bikes) so you can stand over the top tube safely.

Estimated stack ≈ frame size (cm) × 10 (a 56 cm road frame ≈ 560 mm stack), adjusted slightly by bike type — lower for time-trial, taller for gravel and touring. Estimated reach is a rough rider target from your torso and arm proportions, calibrated so a typical 178 cm rider lands near 390 mm. Both are first-order estimates: confirm against the manufacturer geometry chart before buying.

Frequently Asked Questions

Related Calculators

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Stack and Reach Calculator

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Calculate the stem length needed for your ideal reach.

Crank Length Calculator

Find optimal crank length based on leg length and riding style.

Last updated: 2025-02-20

All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.