Most "what size bike" calculators ask your height and stop. Real fit is more nuanced: torso length, arm length, hip mobility, and riding style all change the answer. This estimator uses four body measurements plus flexibility to recommend a frame size and key geometry targets, then compares to popular 2024-2026 bike models so you know what to actually buy.
| Bike | Reach | Stack | Fit Δ reach | Fit Δ stack |
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Numbers are representative geometry for a size close to your frame recommendation, from manufacturer spec sheets.
Two riders of the same height can differ by 5 cm in torso length and 4 cm in arm length. That's a frame size different. Using only height to choose a bike is one of the most common ways riders end up on a frame that's "almost right" and never quite gets comfortable.
Stack and reach matter more than the seat-tube length printed on the frame. Stack is how tall the front of the bike is; reach is how long. A given reach with a tall stack feels very different from the same reach with a low stack — the first is endurance, the second is race.
If your stack is the limiting factor, go with the larger frame and add spacers. If your reach is the limiter, go smaller. Most modern geometries can be adjusted with stem length and spacer stacks, so a small mismatch is fixable.
Reach and stack describe the frame; your stem length changes effective reach. A 100 mm stem + medium frame can feel the same as a 110 mm stem + small frame in terms of effective cockpit length.
No. A professional fit uses motion capture and dynamic measurements. This calculator gives you a confident starting point before you buy — which is the part most riders get wrong.
This calculator was built to answer a question most online versions skip or oversimplify. It runs entirely in your browser; no inputs are stored or transmitted. The math is grounded in standard cycling physics and physiology models, and is suitable for hobbyist and intermediate training use. It is not a substitute for a coach, sports scientist, or professional bike-fit service.
This tool does not collect personal data. All inputs and results stay in your browser. We do not set first-party analytics cookies. This site may display ads served by Google AdSense; Google, as a third-party vendor, uses cookies to serve ads based on a user's prior visits to this site or other sites. Google's use of advertising cookies enables it and its partners to serve ads based on the visit to this site and/or other sites on the Internet. You can opt out of personalized advertising by visiting Google Ads Settings (google.com/settings/ads). Third-party vendors, including Google, use cookies to serve ads based on a user's prior visits to this site or other sites.
Children under 13 are not the intended audience.
This calculator is provided for general informational and educational purposes only. It is not medical, mechanical, or legal advice. Predicted values depend on inputs you supply and simplified physical models; real-world outcomes vary. Use at your own risk. Brand names are descriptive only and do not imply affiliation.