Bike size and fit calculator
Find the right size road, gravel or triathlon bike before you buy, and how to set it up once you have it. Height and inside leg are enough to start.
Optional. Pick a bike you own or like, or leave it on any brand.
More precise: flexibility and shoulders (optional)
Lie on your back, hold one thigh upright with both hands, then straighten that knee as far as you can. How far does it go? This sets how low your bars can go.
Enter your height and inside leg to see your size.
Buying: compare stack and reach
A "56" or a "medium" means something different at every brand. Two numbers do not:
- Stack is how high the top of the head tube is above the bottom bracket. More stack means higher handlebars and a more upright position.
- Reach is how far it is in front of the bottom bracket. More reach means a longer, more stretched position.
Open the geometry chart for the bike you like and pick the size closest to your numbers. Reach matters most: a stem can only fix about 2 cm either way, and spacers about 3 cm of stack.
How to measure yourself
Wear cycling shorts or close-fitting clothes, no shoes. Measure each one twice and use the average.
- Height. Barefoot, back against a wall, looking straight ahead. Lay a book flat on your head, mark the wall under it and measure from the floor.
- Inside leg. Barefoot, back to the wall, feet about 15 cm apart. Pull a hardback book up firmly between your legs, spine up, as a saddle would sit. Measure from the floor to the top of the spine.
- Shoulder width. Find the bony point at the outside of each shoulder and measure straight across between them. A second person makes this much easier.
Road, gravel or triathlon
- Road race bikes are lower and longer, for speed. Road endurance bikes have a taller front end and shorter reach, easier on the back over long rides.
- Gravel bikes sit taller still, with shorter stems and wider bars for control off road. Gravel brands differ the most, so check stack and reach carefully.
- Triathlon and TT bikes have a steeper seat angle that rolls you forward, so the saddle sits further forward and the front end much lower and longer. Armrests and extensions adjust a lot, so stack and reach are a guide rather than a hard limit. UCI time trials require the saddle nose to be at least 5 cm behind the bottom bracket; most triathlons do not.
How accurate is this?
Every bike's numbers come from the brand's own website: 150 frames from 25 brands, checked October 2026. Where a brand publishes its own size chart (65 bikes so far, from 3T, BMC, Cannondale, Canyon, Giant, Lauf, Liv, Orbea, Ribble, Rose, Trek and Van Rysel), we follow it: you get a size the brand recommends for your height, and where two sizes overlap, your inside leg picks between them. Only if your build is far from what the chart assumes do we go by the frame measurements instead.
For every other bike we work from the frame measurements, matched to targets fitted to all those brand charts. Tested on each brand with that brand left out of the fit, it picks the brand's own size 69% of the time, and the brand's size or the next one 98% of the time. That is close to as good as it gets, because brands disagree with each other: for a 177 cm rider, the Trek Madone size Trek recommends has a front end about 2 cm taller than the Canyon Ultimate size Canyon recommends, with the same reach.
What it cannot know:
- How you like to sit. It aims for a typical position for your height.
- Your own body beyond height, inside leg and hamstrings. Studies of trained riders found that arm length, for example, does not predict how far people reach, so we do not ask for it.
- Triathlon bikes, where armrests and extensions change the fit a lot. These numbers are the least certain.
Use it to narrow down the size and compare bikes. Before spending a lot, test ride the size, or book a bike fit if you have pain or are buying a tri bike.
What the research says
- A study of 50 trained road cyclists on their own, pain-free bikes found their bars sat on average 13% of saddle height below the saddle, and that reach followed height: arm length did not predict it. Of the flexibility tests, only hamstring flexibility predicted how low riders had their bars; touching your toes did not (Holliday and Swart, 2021). We use all three findings.
- When three riders each went to nine professional fitters, the recommended saddle heights and setbacks were up to 3 cm apart, while the LeMond saddle height formula we use landed within 1 mm of the fitters' average (Braeckevelt and others, 2019). Even expert fits differ by a few centimetres, so treat any single number, ours included, as a starting point.
How this is worked out
Your size comes from the height and inside leg charts of Specialized, Canyon and Trek, which agree to within a couple of centimetres. Stack and reach come from a formula we fitted to the published geometry of twelve popular bikes, three of each type, such as the Specialized Tarmac, Canyon Endurace, Trek Checkpoint and Cervélo P5. For road race bikes it lands within about 5 mm of the real frames.
"Bikes that fit you" compares your numbers with every size of the bikes we have measured. For each size we work out the stem that puts the bars at your reach and how much higher or lower they need to be, then pick the size that needs the least change. When two sizes are close we show both and lean to the smaller one.
If your legs are long or short for your height, we raise or lower the bars to keep them the same share of saddle height below it, and hamstring flexibility moves them about 1 cm either way, both from the study above. Saddle height uses the LeMond formula. Setback, stem and bar width are typical starting points, and the drop on endurance, gravel and tri bikes is our own estimate. A professional bike fit is worth it if you have pain or are buying a tri bike.