Bike Fit is a new tool in Stamptivity. Add your body measurements and a bike's geometry chart, and it tells you how that bike fits, which setup to start from, and what to change on a bike you already ride. It works for a bike you're thinking of buying as well as the one in your garage.

Size labels don't mean much across brands: one brand's M can ride like another's S. Bike Fit ignores the label and works from the numbers that decide your position on the bike: stack, reach, and the seat and head tube angles.

How it works

You. Height and inseam are enough to start. Add torso, arm length and shoulder width for a more confident result, then pick your riding style and flexibility.
Your bike. Paste the manufacturer's geometry chart or type the numbers in. Add your current stem, spacers, handlebar and saddle if you know them.
Fit result. See how the bike fits, the setup to start from, and a list of what to adjust.

Fit result, factor by factor

Each factor is shown on its own with its value and a short explanation. There is no hidden overall score.

Standover: clearance between your inseam and the top tube.
Seatpost showing: how much seatpost your saddle height leaves exposed, and whether it fits within the frame.
Position: where your hands end up compared with where your body wants them, both further or closer and higher or lower.
Cockpit: the stem and spacers needed to reach that position, and whether they're typical parts or an unusual setup.
Handling: trail, computed from head angle, fork offset and wheel size.
Confidence: how much the result depends on measurements you haven't entered yet.

Technical terms in the results have a dashed underline. Hover over one, or tap it on your phone, for a plain-language explanation.

Recommended setup and what to adjust

For each bike you get a starting setup: saddle height, saddle setback, stem length and angle, spacers, and a handlebar width suggested from your shoulders. Enter your current setup and the recommendation turns into concrete changes, such as "raise the saddle about 10 mm" or "hands are about 15 mm too far", along with the stem and spacers that would fix it.

Add bikes in seconds

Copy the geometry table from a manufacturer's website and paste it in. Bike Fit reads sizes laid out across or down, values in mm or cm, and labels in several naming styles. It also picks up stock stem, crank and bar-width rows when the chart has them. Before you add anything, a preview shows exactly what was read, what wasn't, and whether the chart's numbers agree with each other. Pick the sizes you want and each one becomes a bike.

Honest about uncertainty

Measuring yourself is never exact. Any measurement can be a single value, a min–max range, or three repeat readings, and parts you don't know, such as spacer height, fall back to marked estimates. That uncertainty is carried through every calculation, so each result shows its range, not only one number. The tool also tells you which missing measurement would narrow the result the most.

Handlebars modelled properly

Drop bars are modelled with their reach, drop and rotation, so hood and drop positions follow the actual bar. They're drawn to scale in the side view, and flat bars are supported too.

When you need more

Compare bikes: put sizes or models side by side, factor by factor, each fitted to your measurements.
Adjust & Compare: try stems, spacers, handlebars and saddle positions and see the effect in millimetres and on a same-scale side view. Compare against your measurements or another bike, copy another bike's setup, or match its position. Save variations as scenarios to come back to.
Report: one printable page with your measurements and their reliability, each bike's fit and recommended setup, risks, what to measure next, and what can't be concluded.
Export and import: save everything as a JSON file and load it on another device.
Assumptions and formulas: every formula and default the tool uses is listed on the page.

Private by design

Everything runs in your browser. Your measurements and bikes are saved on your device only and are never uploaded.

Bike Fit is a geometry-based starting point, not a professional bike fit. It can't see your flexibility, pedalling or any pain. If something hurts, see a fitter before making big changes. For a walkthrough, read the Bike Fit guide, or open Bike Fit and load the example to see it in action.

New tool: see how a bike fits you and what to adjust.