What size bike do I need?

Height and inseam in, a starting size out.

Monsoon Cycles, Colorado Springs · Updated August 21, 2026

Measure your inseam properly first: barefoot, back against a wall, a hardcover book snug where the saddle goes, floor to the top of the book. Do not use your pants size.

The math

Road frame size is inseam × 0.665 in centimeters, the traditional center-to-top rule. Saddle height is inseam × 0.883, Greg LeMond's formula, which is a starting point that real fits then move around. The letter size is binned from the frame number the way most modern brands do it.

What a chart does not know

A size chart uses two numbers. It does not know your flexibility, your reach, how long your femurs are, what hurts after two hours, or what the bike is for. Between two adjacent sizes, the right answer depends on all of that, which is why the output here is a starting size. If you are between sizes or buying anything expensive, a real fit costs $150 and settles it.

Modern bikes come in three to six sizes, often five. Ask yourself: do people come in five sizes? I don't think so, and that, more than anything, is why I build custom frames. If no stock size fits you well (long legs, short torso, or the reverse), that is what custom frames are for. You can sketch that frame yourself in the Frame Lab right now, or email Austin to get started.