Enter your measurements and a bike’s geometry to see how it fits, which saddle height, stem and spacers to start from, and what to adjust on a bike you already ride. Size labels differ between brands — this works from stack, reach and angles instead. Comparing sizes or bikes is there when you need it.
A geometry-based starting point, not a professional bike fit. Every output is a starting-point estimate with its uncertainty shown. It can’t see your flexibility, pedalling or any pain — if something hurts, see a fitter before making big changes.
Height and inseam are enough to start. Enter a range whenever you’re unsure — the uncertainty is carried through every result.
Measurement check
Height is required for the proportion checks and for estimating torso and arm length.
Inseam is required — it sets the saddle height estimate and standover checks.
Estimated from height and inseam. Measuring it narrows the hand-position target.
Estimated from height. Measuring it narrows the hand-position target.
The bike you ride or are thinking of buying, from the manufacturer’s geometry chart. One is enough; add more to compare sizes or models.
Add the bike you ride or want to buy from the manufacturer’s geometry chart (search “[model] geometry”). The quickest way: copy the whole table and paste it — every size is read at once. Or pick one of the charts already typed in, or enter stack, reach and the two tube angles by hand.
Bike Fit takes your body measurements and a bike’s geometry chart and tells you how that bike fits: how much standover and seatpost you have, where your saddle and hands will end up, and whether an ordinary stem and spacer setup gets them where they should be. It then gives a starting setup — saddle height, saddle setback, stem length and angle, spacers and, for drop bars, a handlebar width — and, if you enter the setup you ride now, exactly what to change.
It works from stack, reach and the tube angles rather than the size on the sticker, because a size M from one brand can be longer and lower than an L from another. Measurements can be entered as ranges, and every result shows its uncertainty instead of a falsely precise number.
When you need more, add more bikes to compare sizes or models side by side, and use Adjust & Compare to try stems, spacers and handlebars — against your measurements or against a bike that already feels right. Everything stays in your browser.
Enter your height and inseam and the bike’s geometry (stack, reach and the two tube angles are enough). The tool checks standover and seatpost, and whether an ordinary stem and spacer setup can put your hands where they should be — something a height chart can’t tell you. If it takes an unusually short or long stem, that’s a sign the size is at the edge for you.
Add the bike and enter its current saddle height, setback, stem and spacers. The fit result compares them with the recommended range and gives concrete changes, such as raising the saddle 10 mm or fitting a shorter stem — or confirms that a value is already in range.
Saddle height from inseam (the LeMond method) is a reasonable starting point, usually within about 1–2 cm. Where your hands should be is less certain because it depends mostly on how upright you like to sit, so it is shown as a range, with a confidence of Medium at best and only when your torso and arm are measured. If you own a bike that already feels comfortable, compare against it in Adjust & Compare — its position is real evidence of what works for you.
Stack and reach locate the top of the head tube. Headset cap, spacers, stem length and angle, bar rise and bar reach all sit on top of that point, and the steerer leans back, so 20 mm less stack rarely means exactly 20 mm lower hands. The simulator shows where each millimetre comes from.
No. It gives a geometry-based starting point with its uncertainty shown. A professional fitter sees your flexibility, pedalling and any pain, which no calculator can. If something hurts, get a fit before making big changes.
No. Measurements, bikes and saved scenarios are stored in your browser only. You can export them as a JSON file and import them on another device.