Bike size calculator: find your bike frame size by height and inseam

Built by Nitin Raja · Last updated October 24, 2026

This bike size calculator gives the frame size that fits your body for road, gravel, hybrid, mountain and kids' bikes. Bike sizes are written in different ways: road bikes by frame size in centimetres (a 54 or a 56), mountain and hybrid bikes mostly by letters (S, M, L) and sometimes inches, kids' bikes by wheel size. The calculator uses your height for every type and your inseam, the length of your legs, to sharpen road and gravel sizes, choose between two letter sizes and give a starting saddle height. The bike size charts below show the same numbers by height, and the guide explains road bike size, stack and reach, the difference between brands and what to check on a test ride. Nothing is stored, and the share link keeps your inputs.

How does the bike size calculator work?

For road and gravel bikes it estimates the frame size twice. From your height, using a curve through typical brand size charts (50 cm at 160 cm tall, 53.5 at 170, 56.5 at 180, 59 at 190). From your inseam, using the classic rule frame size = 0.665 x inseam. With both, it takes the average and rounds to a whole size. Mountain and hybrid bikes are sold by letter size for a range of rider heights; when you are within 2 cm of the next size, your inseam decides (long legs for your height go up, short legs go down). Kids' bikes use woom's published height ranges per wheel size. The saddle height is 0.883 x inseam, a starting point popularised by Greg LeMond.

Worked example. A rider 180 cm tall (5′ 11″) with an 84 cm (33 in) inseam wants a road bike. From height: 56.5 cm. From inseam: 0.665 x 84 = 55.9 cm. Average: 56.2, so a 56 cm frame, usually sold as a M/L or L. Saddle height: 0.883 x 84 = 74.2 cm from the centre of the crank to the top of the saddle.

How to find your bike size: step by step

1. Choose the type of bike

Pick road, gravel, hybrid, mountain or kids. Road and gravel bikes are sized by frame size in centimetres, hybrid and mountain bikes mostly by letter size (S, M, L), kids' bikes by wheel size.

2. Enter your height

Type your height in centimetres or feet and inches, measured barefoot. Height alone gives a good first size for every type of bike.

3. Measure and add your inseam

Stand barefoot with your back to a wall, put a hardback book between your legs spine up, pressed gently upwards like a saddle, and measure from the floor to the top of the spine. Enter it in centimetres or inches: it sharpens the road and kids' sizes and gives a saddle height.

4. Check the brand chart and test ride

Compare the result with the size chart of the bike you like: brands size differently. If you are between two sizes, test ride both, or compare their stack and reach numbers.

How to measure your inseam for a bike

Your cycling inseam is not your trouser inseam: it is measured to the crotch bone, with pressure like a saddle. Take off your shoes and stand straight with your back to a wall, feet about 15-20 cm apart. Push a hardback book up between your legs, spine up and level. Mark the wall at the top of the spine, step away and measure from the floor to the mark. Do it twice; the two readings should agree within a centimetre. If you do not have a tape measure, the online ruler can check a shorter length, and our guide on measuring your height at home uses the same wall-and-book idea.

Bike size chart

Pick the chart for your type of bike. Heights are barefoot; sizes are the typical range across brands.

Road bike size chart (and gravel)

Mountain bike size chart

Hybrid bike size chart

Kids' bike size chart

Road chart: this calculator's height curve, with the inseam that gives the same frame by the 0.665 rule. Mountain and hybrid: typical letter-size ranges across brands. Kids: woom's published height and inseam ranges.

Road bike size: what the frame number means

A road bike sold as a "56" traditionally has a seat tube 56 cm long, measured from the centre of the crank axle to the top of the seat tube (or to the centre of the top tube on some brands). Modern road frames have sloping top tubes and short seat tubes, so many brands now label sizes by a nominal number or by letters and publish rider height ranges instead. That is why a 56 from one brand can be a 54 or a 58 somewhere else. Trek's Domane chart, for example, puts riders of 5′ 9″-5′ 11″ on a 56 and 5′ 11″-6′ 1″ on a 58, about one size larger than the typical chart here.

Mountain bike size by height

Mountain bikes are sized by letters, and modern ones have long reach and short seat tubes so a long dropper post fits. The rider-height ranges overlap between brands by a few centimetres. If you are between sizes, the larger bike is more stable at speed and on descents, the smaller is easier to throw around on tight trails. Check standover: you should be able to stand over the top tube with a few centimetres of clearance.

Hybrid and city bike size

Hybrid bikes sit upright with flat handlebars, so fit is more forgiving than on a road bike. They are sold in letters, often with a frame number in inches or centimetres. Choose by height first; if the bike has a step-through frame, standover is not a concern and you can pick on reach and comfort.

Gravel bike size

Gravel bikes use road-style sizing (cm or letters) with a slightly more relaxed position. Most riders take the same size as on a road bike from the same brand. Between sizes, many choose the smaller frame for control on rough ground and adjust the stem.

Kids' bike size by age and height

Children grow, but a bike that is too big is harder to control and less fun. Size by height and inseam rather than age: the child should be able to put both feet on the ground (balance bikes and first pedal bikes) or at least the balls of both feet (bigger kids), and reach the brake levers easily. Age only helps as a rough guide, because children of the same age can differ by 20 cm in height.

Stack and reach, briefly

Stack is the vertical distance from the centre of the crank axle to the top of the head tube; reach is the horizontal distance between the same two points. Together they describe how high and how far forward the handlebars sit, independent of how a brand labels its sizes. A higher stack gives a more upright position, a longer reach a more stretched one. When two sizes are close, compare their stack and reach with a bike that already fits you: a difference of 1 cm or less is easy to adjust with the stem and spacers.

Between two sizes: size up or down?

Long legs for your height (an inseam above about 48% of your height) often suit the larger size, short legs (under about 44%) the smaller, and the calculator applies that rule to letter sizes. Flexibility, riding style and comfort matter too: a smaller frame gives a more upright, nimble ride and is easier to adjust longer, a larger frame is more stretched out and stable. If you can, test ride both.

Saddle height from your inseam

Once the frame size is right, saddle height makes the biggest difference to comfort. A common starting point is 0.883 x inseam, from the centre of the crank axle to the top of the saddle along the seat tube. Another is 109% of inseam measured from the pedal at its lowest point, from a 1967 study by Hamley and Thomas. Both are starting points: adjust in small steps until your knee is slightly bent at the bottom of the stroke and your hips do not rock.

Test ride checklist

• You can stand over the top tube with clearance (more on a mountain bike).
• With the saddle at your height, you reach the bars with a slight bend in the elbows and without locking your arms.
• You can reach and pull the brake levers comfortably.
• Your knee does not hit the bars when turning slowly, and your toes do not hit the front wheel more than barely.
• After 10-15 minutes, no pain in hands, neck or lower back.

Why we built this bike size calculator

Before building CheckMyHeight, I tested a lot of height and sizing websites to see what people actually need from them and what just gets in the way. Bike sizing is confusing for a simple reason: there is no single size system. Road and gravel frames are sold in centimetres, mountain and hybrid bikes in letters (S, M, L) with older frames in inches, and kids' bikes by wheel size. Each brand's chart covers only its own models, and the same rider can be a 54 at one brand and a 56 at another. Height-only charts also miss leg length, which is what decides between two sizes for many riders.

We wanted one calculator that covers the common bike types, uses your inseam when you have it, adds the saddle height that goes with it, and explains every number, so you arrive at a shop or a brand's geometry chart with a sensible shortlist.

What this bike size calculator measures

You choose the bike type and enter your height; the inseam is optional and can be in cm or inches. The code then does this:

• Road and gravel: a frame size from your height, read off a curve through typical brand charts (47 cm at 150 cm tall up to 62 cm at 200 cm), and one from your inseam by the classic rule, 0.665 x inseam. With both, it uses the average, shown as a range of plus and minus 1 cm with the matching letter size.
• Mountain and hybrid: the letter size for your height from a height table, with the nominal frame size in inches. Within 2 cm of the next size, it names both, and long or short legs for your height decide which to try first.
• Kids: every wheel size (12 to 26 inches) whose published height range from the bike maker woom includes the child, with the inseam used to step down when the legs are short.
• Saddle height: 0.883 x inseam, from the centre of the bottom bracket to the top of the saddle (Greg LeMond's rule), for adult bikes.

The tables were last checked on 24 October 2026, and the worked example on this page is an automated test the maths must pass before the site is published. What it does not measure: a model's stack and reach, your arm and torso length, flexibility, or the riding position you prefer. Every brand's own geometry chart overrides this result, and a professional bike fit goes further than any calculator.

Why this bike size calculator is different

• It starts empty. No bike type or height is chosen for you, and no size appears until you enter yours.
• Five bike types in one place: road, gravel, hybrid, mountain and kids.
• Height and inseam together, with both estimates shown, plus the saddle height.
• The rules are named on the page (0.665 x inseam, 0.883 x inseam, woom's height ranges), so you can check them.
• A share link restores your inputs, there is no account, and it all runs in your browser.

How accurate is this bike size calculator?

For most riders the result lands on the right size or the next one. The two estimates (height and inseam) agree within about a centimetre for average proportions; when they do not, the average is a better guide than either alone. Brand differences are bigger than the calculator's error: the same rider can be a 54 at one brand and a 56 at another. Use the size here to narrow the choice, then the brand's own chart and a test ride to decide. A professional bike fit is worth it if you ride long distances or have discomfort.

Sources

• Trek Domane size chart (rider height and inseam per frame size), as listed by Trek dealers such as Ridley's.
• woom kids' bike size chart (height and inseam per model and wheel size), as published by woom dealers such as Wheelbase.
• Greg LeMond and Kent Gordis, Greg LeMond's Complete Book of Bicycling (1987): saddle height = 0.883 x inseam.
• Hamley EJ, Thomas V. Physiological and postural factors in the calibration of the bicycle ergometer. Journal of Physiology 1967; 191: 55P (109% inseam saddle height).
• Bicycle frame (Wikipedia): frame geometry, stack and reach.

Related tools

• How to measure your height - at home, to the nearest centimetre.
• Ski size calculator - ski length for your height plus an indicative DIN setting.
• Snowboard size calculator - board length and width from height, weight and boot size.
• Desk height calculator - sitting and standing desk heights for your body.
• Height percentile calculator - how a child's or adult's height ranks.