How we size
Every size on gearsizing comes from a published chart or formula. This page lists each one, where it comes from and when we last checked it.
Brand charts beat formulas
When a brand publishes a chart for a model, we use its rows as they are.
One size, and the reason
Charts disagree by about one size, so you get a size to start with, the one either side when you’re close, and why.
No source, no rule
Anything we can’t source stays off the page until we can.
The rules, sport by sport
| Gear | What decides the size | Then | Sources |
|---|---|---|---|
| Adult bikes | Height picks the size band (seven bands, 148–200 cm) | Road: inseam × 0.665 = frame in cm, and it settles a between-sizes answer. Mountain: inseam × 0.226 = seat tube in inches, as a check. Saddle: inseam × 0.883. | S1–S6 |
| Kids’ bikes | Inseam picks the wheel (12″–26″) | Never a wheel bigger than the inside leg. New riders start on the smallest wheel that fits, confident riders the largest. Seat height by rider stage. | S7–S10 |
| Snowboards | Weight sets the length range | Height checks it; ability and style pick the spot; boot size picks the width. | S11–S12 |
| Kids’ snowboards | Height and weight | Between chest and chin. | S13 |
| Skis | Height − 12 cm (beginner), − 2 (intermediate), + 5 (expert) | ± 5 cm for weight and terrain. | S14–S15 |
| Kids’ skis | Height and weight | Between chest and nose. | S16 |
Sources
Each chart was read on the brand’s or shop’s own page. We re-check every source at least once a year.
| # | Source | What we use | Checked |
|---|---|---|---|
| S1 | Specialized size guide | Rider height to size for every current model | 30 Oct 2026 |
| S2 | Canyon Endurace geometry | Rider height to 3XS–2XL, seat tube and standover | 30 Oct 2026 |
| S3 | bike-discount.de frame size calculator | Mountain: inseam × 0.226; road height to frame | 30 Oct 2026 |
| S4 | calculate.co.nz bike size calculator | Road × 0.665, hybrid × 0.685, saddle × 0.883 | 30 Oct 2026 |
| S5 | evo mountain bike size chart | Rider height to XS–XXL; sizing up or down | 30 Oct 2026 |
| S6 | REI bike fit | Standover clearance | 30 Oct 2026 |
| S7 | REI kids' bikes | Wheel size by height, inseam and age | 30 Oct 2026 |
| S8 | Two Wheeling Tots kids' bike sizing | Wheel size; seat height by rider stage | 30 Oct 2026 |
| S9 | woom size guide | Inseam and height per woom model | 30 Oct 2026 |
| S10 | Cycling UK | Wheel no bigger than the inside leg | 30 Oct 2026 |
| S11 | evo snowboard size chart | Height and weight to length; boot to width | 30 Oct 2026 |
| S12 | REI snowboards | Weight to length; boot to width | 30 Oct 2026 |
| S13 | Snow+Rock kids' snowboards | Age, height, weight to length | 30 Oct 2026 |
| S14 | evo ski size chart | Height to length by ability | 30 Oct 2026 |
| S15 | REI downhill skis | Height to length by ability | 30 Oct 2026 |
| S16 | evo kids' skis | Age, height, weight to length | 30 Oct 2026 |
| S17 | Trek Domane AL size guide | Rider height and inseam to frame size | 31 Oct 2026 |
| S18 | Trek Marlin size guide | Rider height and inseam to 2XS–2XL | 31 Oct 2026 |
| S19 | Giant Defy Advanced 2 sizing guide | Rider height to XS–XL | 31 Oct 2026 |
| S20 | Giant Talon 2 sizing guide | Rider height to XS–XL | 31 Oct 2026 |
| S21 | Cannondale Synapse size finder | Rider height to frame size | 31 Oct 2026 |
| S22 | Scott Speedster size chart | Body height to XXS–XXL | 31 Oct 2026 |
| S23 | Orbea Orca size guide | Rider height to frame size | 31 Oct 2026 |
| S24 | Liv Avail AR sizing guide | Rider height to XS–L (women’s) | 31 Oct 2026 |
What we don’t do
- We don’t copy brands’ charts, images or PDFs. We restate the numbers in our own tables and link to the original.
- We don’t change a size because a shop pays us. Shop links never affect the answer.
- We don’t collect your measurements. The calculators run in your browser, which remembers the last ones you typed so the next calculator starts from them.
Found a size that doesn’t match a brand’s current chart? Tell us with a link to the chart and we’ll check it.