Bike Size Calculator
Road bike size chart (seat tube, c-t)
| Height | Frame cm | Letter |
|---|---|---|
| 5'1"–5'5" (155–165cm) | 47–50 | XS |
| 5'4"–5'7" (163–170cm) | 50–52 | S |
| 5'6"–5'10" (168–177cm) | 52–55 | M |
| 5'9"–6'0" (175–183cm) | 55–57 | L |
| 5'11"–6'3" (181–190cm) | 57–60 | XL |
| 6'2"+ (188cm+) | 60+ | XXL |
Mountain bike size chart
| Height | Frame inches | Letter |
|---|---|---|
| 4'11"–5'4" (150–162cm) | 13–14" | XS |
| 5'3"–5'8" (160–172cm) | 15–16" | S |
| 5'7"–5'11" (170–180cm) | 17–18" | M |
| 5'10"–6'2" (178–188cm) | 19–20" | L |
| 6'1"+ (186cm+) | 21"+ | XL |
How to measure your inseam (1 minute)
Stand barefoot with your back against a wall, feet shoulder-width apart. Hold a hardcover book between your legs, spine up, pressed firmly against your crotch (simulating saddle pressure). Have someone measure the vertical distance from the top of the book spine to the floor. Riders of the same height can differ by ±5cm of inseam — one to two frame sizes — so measure, don't guess.
Size gets you the right bike. Fit makes it comfortable.
On the same frame, 1cm of saddle height or stem length changes everything. Upload a side-view riding video — AI measures your knee, hip and torso angles and tells you exactly how to set this bike up.
Upload a video, start the analysis ›FAQ
What if I only know my height?
Height-only works (inseam estimated at height × 0.45) but can be off by a full size. Leg-long and torso-long riders of identical height can need frames two sizes apart — measure if you can.
Between two sizes — up or down?
Most riders: size down. A smaller frame adjusts up with stem and spacers; an oversized frame has no way back. Size up only for a deliberately upright, relaxed position.
Is Medium the same across brands?
No — same letter, up to 1–2cm different stack/reach. Always check the brand's geometry chart before ordering.
Related: Saddle height calculator · FTP to W/kg converter · Crank length guide · AI vs in-person fitting