Bike Size CalculatorFrame Size by Height & Inseam for Road, Gravel, Mountain, Hybrid & Kids’ Bikes
Enter your height and inseam and get your frame size for every type of bike. You also get your saddle height, the standover clearance to look for, a typical crank length, and clear advice if you fall between two sizes.
Frame formula from the LeMond inseam method · height charts per Trek’s published sizing · saddle height per LeMond (0.883) and Hamley (109%) · Last reviewed 23 October 2026
You & your ride
Bike typeBarefoot, a book pressed firmly up into your crotch, floor to the top of the spine.
Arm span & riding style (optional)
Your road bike size
56 cmM/L
Your size on every type of bike
Do the two methods agree?
Between sizes?
Insights
What size bike do I need?
Road and gravel: frame size (cm) ≈ inseam (cm) × 0.665. A rider with an 84 cm inseam needs about a 55.9 cm frame, which matches the 174–180 cm height band on Trek’s chart. Mountain bikes: frame size (in) ≈ inseam (cm) × 0.225, so about 18.9″, usually sold as a Large.
Use height to choose the size, and inseam to confirm it. If the two disagree, your proportions decide: long legs favour the larger frame for saddle height, and a long torso and arms favour it for reach.
How to use the bike size calculator
- Choose the type of bike. Road, gravel, mountain, hybrid or kids. Each is sized differently: road bikes in centimetres, mountain and hybrid bikes in letters or inches, and kids’ bikes by wheel size.
- Enter your height. In centimetres, or feet and inches.
- Measure your inseam. Stand barefoot against a wall, pull a hardback book firmly up between your legs as if it were a saddle, and measure from the floor to the top of the book’s spine. Repeat twice and use the average.
- Add your arm span (optional). If your arms are long or short for your height, the calculator adjusts its between-sizes advice for reach.
- Read the results. You get your recommended size for every bike type, your saddle height, the standover to look for and a typical crank length, all drawn to your proportions.
Bike size formulas
Road / gravel frame (cm) = inseam (cm) × 0.665 (LeMond)
MTB / hybrid frame (in) = inseam (cm) × 0.225
Saddle height, BB → saddle = inseam × 0.883 (LeMond)
Saddle height, pedal → saddle = inseam × 1.09 (Hamley 109%)
Max standover height = inseam − clearance (2.5 cm road · 5 cm MTB)
Ape index = arm span − height
Frame “size” is traditionally the seat-tube length, measured from the centre of the bottom bracket. Modern frames have sloping top tubes, so brands now size by stack and reach. That’s why a 56 from one brand can fit like a 54 from another. Use this calculator to get into the right band, then compare the brand’s own size chart.
Worked example: 178 cm tall, 84 cm inseam
- Road frame: 84 × 0.665 = 55.9 cm → 56 cm (M/L). The height chart agrees: 178 cm falls in the 174–180 cm band for a 56.
- Mountain bike: 84 × 0.225 = 18.9″ → Large (177–188 cm on the height chart).
- Saddle height: 84 × 0.883 = 74.2 cm from the centre of the bottom bracket to the top of the saddle, or 84 × 1.09 = 91.6 cm from the pedal spindle with the crank at the bottom.
- Standover: look for a road frame with standover below about 81.5 cm.
These are the calculator’s default inputs, so you can check every number above.
Road bike size chart by height and inseam
Based on Trek’s published road sizing. The “inseam formula” column shows what 0.665 × inseam gives at each end of the range, so you can see how closely the two methods agree.
| Frame size | Letter | Rider height | Inseam | Inseam formula (×0.665) |
|---|---|---|---|---|
| 49 cm | XS | 156–163 cm (5′1″–5′4″) | 74–77 cm | 49.2–51.2 cm |
| 52 cm | S | 163–168 cm (5′4″–5′6″) | 76–79 cm | 50.5–52.5 cm |
| 54 cm | M | 168–174 cm (5′6″–5′9″) | 78–82 cm | 51.9–54.5 cm |
| 56 cm | M/L | 174–180 cm (5′9″–5′11″) | 81–85 cm | 53.9–56.5 cm |
| 58 cm | L | 180–185 cm (5′11″–6′1″) | 84–87 cm | 55.9–57.9 cm |
| 61 cm | XL | 185–191 cm (6′1″–6′3″) | 86–90 cm | 57.2–59.9 cm |
Mountain bike size chart by height
Mountain bikes are sized in letters. Modern trail bikes are longer, so many riders between sizes now choose the smaller frame for agility, or the larger one for stability at speed.
| Size | Rider height | Feet & inches | Typical inseam | Frame (×0.225) |
|---|---|---|---|---|
| XS | 145–155 cm | 4′9″–5′1″ | 65–73 cm | 14.7–16.4″ |
| S | 155–165 cm | 5′1″–5′5″ | 70–78 cm | 15.7–17.4″ |
| M | 165–176 cm | 5′5″–5′9″ | 74–83 cm | 16.7–18.6″ |
| M/L | 173–180 cm | 5′8″–5′11″ | 78–85 cm | 17.5–19.0″ |
| L | 177–188 cm | 5′10″–6′2″ | 80–88 cm | 17.9–19.9″ |
| XL | 188–195 cm | 6′2″–6′5″ | 85–92 cm | 19.0–20.6″ |
| XXL | 195–203 cm | 6′5″–6′8″ | 88–95 cm | 19.7–21.5″ |
Hybrid and fitness bikes (such as the Trek FX family) use similar letter bands, so the same chart is a good starting point.
Kids’ bike size chart: wheel size by height and inseam
Kids’ bikes are sized by wheel diameter. Inseam matters most: a beginner should be able to put the balls of both feet on the ground with the saddle at its lowest setting.
| Wheel size | Typical age | Child height | Inseam |
|---|---|---|---|
| 12″ | 2–3 yrs | 34–40 in (86–102 cm) | 35–42 cm |
| 14″ | 3–4 yrs | 37–43 in (94–109 cm) | 40–50 cm |
| 16″ | 4–5 yrs | 43–48 in (109–122 cm) | 45–55 cm |
| 20″ | 5–8 yrs | 48–53 in (122–135 cm) | 55–63 cm |
| 24″ | 7–11 yrs | 53–57 in (135–145 cm) | 60–72 cm |
| 26″ | 9–13 yrs | 55–65 in (140–165 cm) | 69–89 cm |
Saddle height by inseam
Set your saddle height first; it matters more for comfort and knee health than the frame size. Two classic starting points:
| Inseam | LeMond (BB → saddle, ×0.883) | 109% (pedal → saddle) | Max road standover |
|---|---|---|---|
| 70 cm (27.6″) | 61.8 cm | 76.3 cm | 67.5 cm |
| 73 cm (28.7″) | 64.5 cm | 79.6 cm | 70.5 cm |
| 76 cm (29.9″) | 67.1 cm | 82.8 cm | 73.5 cm |
| 79 cm (31.1″) | 69.8 cm | 86.1 cm | 76.5 cm |
| 82 cm (32.3″) | 72.4 cm | 89.4 cm | 79.5 cm |
| 85 cm (33.5″) | 75.1 cm | 92.7 cm | 82.5 cm |
| 88 cm (34.6″) | 77.7 cm | 95.9 cm | 85.5 cm |
| 91 cm (35.8″) | 80.4 cm | 99.2 cm | 88.5 cm |
| 94 cm (37.0″) | 83.0 cm | 102.5 cm | 91.5 cm |
From there, fine-tune in 2–3 mm steps. Your knee should keep a slight bend (roughly 25–35°) at the bottom of the stroke, and your hips shouldn’t rock side to side. If they do, the saddle is too high.
Between two sizes? How to choose
- Long legs, short torso (inseam suggests the bigger size): pick the size your height suggests, and raise the saddle. A smaller frame keeps the reach comfortable.
- Long arms or a positive ape index: you can stretch out comfortably, so the larger size suits, especially for racing and long descents.
- Short arms or limited flexibility: size down and fit a slightly shorter stem for an upright, comfortable position.
- Mountain biking: size down for playful, technical riding; size up for stability on fast, rough descents.
A pro tip: it is easier to make a slightly small frame fit (a longer stem, a taller seatpost) than a frame that is too big. If you can’t stand over a frame comfortably, or have to stretch to reach the bars, it is the wrong size whatever the chart says.
Common bike sizing mistakes
- Measuring inseam with shoes on, or reading your trouser inside-leg size. Trouser inseam is usually 5–8 cm shorter than your cycling inseam.
- Comparing sizes across brands. One brand’s 54 can be another’s 56; check stack and reach.
- Using a road chart for a mountain bike. MTB frames have much shorter seat tubes, so the numbers aren’t comparable.
- Buying a kids’ bike to “grow into”. A bike that is too big is hard to control and knocks a child’s confidence. Buy for the inseam they have now.
- Leaving the saddle at the shop height. Set it from your inseam on day one.
Bike size FAQs
What size bike do I need for my height?
For a road bike: 156–163 cm riders usually fit a 49, 163–168 cm a 52, 168–174 cm a 54, 174–180 cm a 56, 180–185 cm a 58 and 185–191 cm a 61. For mountain bikes, 165–176 cm is usually a Medium and 177–188 cm a Large. Confirm with your inseam, because leg length changes the answer.
How do I calculate my bike frame size?
Multiply your inseam in centimetres by 0.665 for a road or gravel bike (result in cm), or by 0.225 for a mountain bike (result in inches). For an 84 cm inseam, that’s about 56 cm for a road bike and 19 inches for a mountain bike.
What size road bike do I need if I am 5’10”?
At 5′10″ (178 cm), most riders fit a 56 cm road frame (size M/L). With an inseam under about 81 cm, a 54 may fit better; above 86 cm, a 58 is worth trying.
What size mountain bike do I need for 5’8″?
At 5′8″ (173 cm), you are at the top of the Medium range and the bottom of M/L on many charts. Choose Medium for agile, technical riding, or M/L for stability at speed, especially if you have long arms.
How do I measure my inseam for a bike?
Stand barefoot against a wall with your feet about 15–20 cm apart. Pull a hardback book firmly up into your crotch, keeping the spine level, and mark the wall at the top of the spine. Measure from the floor to the mark in centimetres, and repeat twice for an average. Don’t use your trouser size; it is usually 5–8 cm shorter.
How high should my bike saddle be?
A good starting point is inseam × 0.883, measured from the centre of the bottom bracket to the top of the saddle (the LeMond method). For an 84 cm inseam that’s about 74.2 cm. Fine-tune until your knee keeps a slight bend (about 25–35°) at the bottom of the pedal stroke.
Is it better to have a bike that is too big or too small?
Slightly small is usually better. A smaller frame can be adjusted with a longer stem and seatpost, but a frame that’s too big can’t be made shorter, and poor standover clearance is a safety risk.
What if I am between two bike sizes?
Look at your proportions. Long arms or a racy position favour the larger size; short arms, limited flexibility or a comfort focus favour the smaller one. For mountain bikes, size down for playful handling and up for stability. A test ride settles it.
How much standover clearance do I need?
Aim for about 2.5–5 cm between the top tube and your crotch on a road bike, around 5–10 cm on a mountain bike, and enough on a hybrid to stand comfortably at junctions. Sloping top tubes make this easier on modern frames.
What size kids’ bike for my child?
Go by inseam first. Typical bands: 12″ wheels for 35–42 cm inseam (age 2–3), 14″ for 40–50 cm, 16″ for 45–55 cm, 20″ for 55–63 cm (age 5–8), 24″ for 60–72 cm and 26″ for 69–89 cm. Beginners should touch the ground with both feet with the saddle at its lowest.
Are bike sizes the same across brands?
No. Frame sizes are labelled differently by each brand, and modern frames are designed around stack and reach, so a 56 from one brand can fit like a 54 from another. Use this calculator to find your band, then compare each brand’s own chart.
What size gravel bike do I need?
Size a gravel bike much like a road bike: inseam × 0.665 gives a good starting point in centimetres. Gravel frames tend to have a taller stack and shorter reach, so if you are between sizes many riders choose the smaller one for control on loose surfaces.
Manzoor Ahmad
Founder, DexoCalc · 13+ years of web development and SEO experience
Manzoor builds and maintains every DexoCalc calculator. For this tool he combined the LeMond inseam formula with Trek’s published height charts and the classic saddle-height methods. He checked where the methods disagree, and generated every chart on this page from the same engine that runs the calculator.
Sources & references
- Trek road bike size chart (frame size by rider height and inseam). scheels.com
- Cyclists Hub. Bike size chart and inseam formulas (road × 0.665, MTB × 0.225) with Trek’s MTB height chart. cyclistshub.com
- Rascal Rides. Kids’ bike size chart by wheel size, age, height and inseam. rascalrides.com
- RoadBikeRider. Which saddle height method is correct? (LeMond 0.883, knee-angle and heel methods). roadbikerider.com
- Hamley EJ, Thomas V. Physiological and postural factors in the calibration of the bicycle ergometer. J Physiol. 1967;191:55P–57P (the 109% inseam method).
Note: Size charts differ by brand, and frames are increasingly sized by stack and reach. Treat these results as a starting point, check the manufacturer’s chart, and test-ride or get a professional bike fit if you can, especially if you have back, knee or hip issues.