Bike size chart gives two sizes: a decision worksheet
GuideKeep missing or conflicting exact-model measurements marked as unknown.
You enter your measurements and the chart returns two sizes. Now what? Keep both on the list and compare the same things on each bike. This worksheet turns "medium or large?" into questions a shop can answer: how low does the saddle go, where can the bars sit, and can you use the brakes comfortably?
First confirm that the overlap is real
Repeat height and cycling inseam measurements. Use the chart for the same model, model year, frame variant and market. Two ranges from different models or years are not an adjacent-size comparison. Check whether both measurements agree with both candidates.
Record where each number came from and when you checked it. Manufacturer-published geometry, your measurement of a bike and a calculator estimate are different evidence. A representative brand reach or an unlabeled frame cannot stand in for the two exact sizes.
Complete this worksheet for each candidate
| Check | Record for each size | What blocks a decision |
|---|---|---|
| Identity and source | Model, year, variant, size, source URL and checked date | Unknown year or conflicting tables |
| Standover and mounting | Published height and measurement location; physical mounting check | Clearance or access unsuitable for the rider and terrain |
| Saddle range | Achievable pedaling height, rail position and insertion limits | Needed position outside the allowed range |
| Cockpit | Frame reach and stack; stem, spacers, bar and hood setup | Position cannot be reached within component limits |
| Controls and handling | Braking, starts, turns, seated and standing control | Controls inaccessible or handling not manageable |
| Riding context | Terrain, duration, luggage, torso/arm proportions and mobility | A static pose is the only evidence for the intended use |
Mark each row checked, missing or conflicting. For a checked row, distinguish acceptable from unacceptable. Missing is not a pass. Ask a shop to measure unpublished saddle limits or arrange a test ride rather than inventing them.
Choose one of four outcomes
Fill out the checks before choosing the outcome. It is easy to prefer a color or a discounted size and then treat every unanswered question as a small adjustment for later. The worksheet is useful precisely because it makes those unanswered questions obvious.
- Size down: all smaller-frame checks pass and the larger frame has a limitation you cannot safely adjust away.
- Size up: all larger-frame checks pass and the smaller frame cannot provide the required position.
- Either size with adjustments: both pass. Write down each setup, compare handling and choose the one that suits your normal riding.
- Not enough evidence: a check is missing, the sources disagree, or neither candidate works. Test ride or consult a fitter; another model may be necessary.
The interactive decision aid on Trek and Canyon chart pages follows this framework. Its manufacturer and test-ride selections describe evidence reported by you, not a model verification performed by BikeSize.
A completed comparison: one size still needs an answer
Here is a fictional shop comparison. The rider falls inside both height and inseam ranges. Both bikes are the same model and year, and the shop has adjusted their saddles for the rider. These figures illustrate how to record a decision; they are not specifications for bikes in our database.
| Check | Smaller frame | Larger frame |
|---|---|---|
| Frame reach / stack | 385 / 560 mm, model chart checked | 395 / 580 mm, same model chart |
| Saddle and standover | Usable position and clearance checked | Usable position and clearance checked |
| Cockpit position | Comfortable after an approved bar-height adjustment | Hoods still feel too far away |
| Proposed change | Existing parts remain within their limits | Different stem suggested; compatibility not yet checked |
| Current result | Passes the completed checks | Unresolved; do not count as passing or failing yet |
At this point the worksheet result is "not enough evidence" for the comparison. The smaller bike has passed, but nobody has checked whether the larger bike's proposed stem change is suitable. You can still choose the already-checked smaller bike; you just cannot claim that the comparison has proved the larger one unsuitable.
Suppose the shop checks the permitted cockpit options and none can provide the required position on the larger frame. The result now supports sizing down. If a suitable change works and the rider is comfortable on a second ride, both sizes remain options. The difference is the completed check, not a new formula.
What would support sizing up?
Reverse the problem. The larger bike offers a comfortable position, while the smaller bike's bars remain too low within the approved setup. Once that limitation is confirmed, sizing up makes sense. This is more specific than saying that larger bikes are comfortable: it identifies the position this rider needs and the frame that can provide it.
Ask a question that can be answered with a measurement
"Will this fit someone my height?" often gets you the same chart again. Instead, send the shop your unresolved row. For example: "My cycling inseam is 79 cm. What is the minimum saddle height on this size with the supplied saddle and post, and where is that measured from?" That asks for a bike dimension rather than another opinion.
For cockpit questions, provide the position you are trying to match if you know it. A fitter's measurement sheet or measurements from a comfortable current bike can help. Do not ask the seller to translate a saddle-to-bar distance directly into frame reach; those are different measurements. The geometry definitions guide shows the reference points.
When the retailer and manufacturer disagree
Check the model year and variant first. An older listing photo, a different wheel setup or an adjustable frame setting may explain the difference. Keep both source links and ask which table describes the bike being sold. If the answer is still unclear, leave the row marked conflicting. Averaging two published numbers produces a third number that neither source actually supports.
A missing value is different from a failed physical check. A shop may be able to measure the actual bike or let you try it. But if you cannot get the measurement, cannot test ride and cannot return the bike reasonably, you are being asked to accept a purchase risk. Name that risk before deciding whether the price is worth it.
Do not buy a frame on the promise of unlimited adjustment
Seatposts have minimum insertion requirements; some frames impose additional insertion restrictions. Saddle clamps must stay inside the marked rail zone. Fork makers limit spacers and stem arrangements. Integrated cockpits may offer fewer practical changes. Use the actual manuals, including torque specifications, and ask a mechanic about compatibility.
Set saddle height and fore-aft position for pedaling before evaluating the handlebars. Moving the saddle forward solely to shorten reach can trade one problem for another. A cockpit adjustment changes hand position, not frame standover, wheelbase or every aspect of steering.
For example, if the smaller frame cannot provide enough handlebar height within the fork's limits, do not mark it acceptable merely because the reach is shorter. If the larger frame is too long even with a suitable cockpit, neither may pass. This is a reason to compare different model geometry.
Apply the road, gravel, MTB and e-bike branches to your worksheet. Persistent pain, numbness, mounting difficulties or uncertain controls are reasons to book a professional fit. Bring the worksheet so the appointment starts with the questions you could not settle.
Frequently Asked Questions
Sources and limits
Reviewed September 17, 2026. Fit and adjustment principles: REI Bike Fitting Basics. Exact limits must be checked in the applicable manufacturer documents, such as Trek manuals. The worksheet is editorial decision support, not a professional fit assessment.