Free bike size calculator
Find the right road, mountain or hybrid bike frame size from your height and inseam, with the size charts and S/M/L labels brands use — updated live, as you type.
On this page14 sections
A sizing guide based on your measurements. Confirm fit on a test ride before buying.
Results are estimates. Consult a professional.
How the bike size calculator works
Frame size is driven by your legs, not your overall height. The bike size calculator works from your inseam — the inside-leg measurement from crotch to floor — because that is what sets how far you can reach the pedals and stand over the top tube. If you only enter your height, the calculator estimates your inseam first, then sizes the frame from it.
Each bike type has its own multiplier. Road frames are quoted in centimetres, mountain frames in inches, and hybrids in centimetres like road bikes. The calculator applies the right one for the bike you pick and returns both a frame number and a size label, updated live, as you type.
What the size label means
Two numbers do the work. The frame size — a centimetre figure for road and hybrid, an inch figure for mountain — is what you match against a manufacturer's geometry chart. The size letter (S, M, L) is the quick label most brands print, useful when a bike is sold by letter rather than by number. Treat both as a starting point, then confirm against the exact model you want to buy.
What goes into your frame size
A frame-size estimate is built from three inputs. Get each right and the recommendation is sound; guess on any one and the bike can feel a size off.
Inseam — the number that matters most
Inseam is your inside-leg length, and it is the single best predictor of frame size. Two riders the same height can have legs that differ by several centimetres, which is enough to shift the recommendation by a full size. If you measure only one thing, measure your inseam.
Height — the fallback input
When you have not measured your inseam, the calculator estimates it as about 47% of your height, then sizes from there. That is accurate enough for a first pick, but it assumes average leg proportions. Long-legged or short-legged riders should measure their inseam rather than rely on height alone.
Bike type — it changes the math
Mountain frames run smaller than road frames for the same rider, because a lower standover height gives clearance on rough ground. That is why the same legs produce a 56 cm road frame but an 18-inch mountain frame. Picking the wrong type gives you the wrong multiplier and the wrong size.
A worked example using the bike size calculator
Maya measures an 84 cm inseam and wants a road bike. She wants the frame size in centimetres and the letter size to look for, before she walks into the shop.
Step 1 — Apply the road multiplier
Road frames use 0.665 of the inseam: 84 × 0.665 = 55.86 cm. Rounded to the nearest whole centimetre, that is a 56 cm frame.
Step 2 — Read off the size label
A 55.86 cm frame falls in the 54–56 cm band, which most road brands label M (medium). So Maya looks for a 56 cm / Medium road frame.
Step 3 — Check the other bike types
If Maya wanted a mountain bike instead, the same inseam converts to inches first: 84 ÷ 2.54 = 33.07 in, then × 0.59 = 19.5 in — an L. A hybrid would be 84 × 0.64 = 53.8 cm, an S.
Bike size chart by height
If you want a ballpark before you measure, these charts give a frame size from your height alone. They are reference tables — the calculator above is more precise because it uses your actual inseam. Road and hybrid frames are in centimetres; mountain frames are in inches.
Road bike size chart
| Rider height | Inseam | Road frame (cm) | Size |
|---|---|---|---|
| 5'0"–5'4" (152–163 cm) | under 69 cm | 47–50 | XS |
| 5'4"–5'7" (163–170 cm) | 69–74 cm | 50–54 | S |
| 5'7"–5'10" (170–178 cm) | 74–79 cm | 54–56 | M |
| 5'10"–6'1" (178–185 cm) | 79–84 cm | 56–58 | L |
| 6'1"–6'4" (185–193 cm) | 84–89 cm | 58–62 | XL |
| over 6'4" (193 cm+) | 89 cm+ | 62+ | XXL |
Road and hybrid frames are measured in centimetres (seat-tube length). Ranges follow the RoadBikeRider and REI road bike size charts.
Mountain bike size chart
| Rider height | Inseam | MTB frame (in) | Size |
|---|---|---|---|
| under 5'3" (under 160 cm) | under 69 cm | 13–14 | XS |
| 5'3"–5'7" (160–170 cm) | 69–74 cm | 15–16 | S |
| 5'7"–5'11" (170–180 cm) | 74–79 cm | 17–18 | M |
| 5'11"–6'2" (180–188 cm) | 79–84 cm | 19–20 | L |
| 6'2"–6'4" (188–193 cm) | 84–89 cm | 21–22 | XL |
| over 6'4" (193 cm+) | 89 cm+ | 23+ | XL+ |
Mountain frames are measured in inches (seat-tube length). Many modern brands sell by letter only; use the calculator's letter when a number is not listed.
Hybrid bike size chart
| Rider height | Inseam | Hybrid frame (cm) | Size |
|---|---|---|---|
| 5'0"–5'4" (152–163 cm) | under 69 cm | 42–47 | XS/S |
| 5'4"–5'8" (163–173 cm) | 69–74 cm | 47–51 | S/M |
| 5'8"–5'10" (173–178 cm) | 74–79 cm | 51–54 | M |
| 5'10"–6'1" (178–185 cm) | 79–84 cm | 54–57 | L |
| 6'1"–6'4" (185–193 cm) | 84–89 cm | 57–61 | XL |
| over 6'4" (193 cm+) | 89 cm+ | 61+ | XL+ |
Hybrid/city frame ranges follow the 0.64 inseam multiplier; some brands quote hybrids in inches instead, so confirm the unit on the model's chart.
How to measure your inseam for a bike
A height-only estimate is fine for browsing, but a measured inseam is what turns it into the right size. The measurement takes five minutes and a book, and it is the step most online size charts skip.
- Take off your shoes and any bulky trousers, and stand with your back to a wall, feet about 15–20 cm (6–8 in) apart.
- Put a hardcover book between your legs, spine facing up, and press it firmly up into your crotch the way a saddle would sit.
- Keep the book level and mark where its top edge meets the wall.
- Measure from that mark straight down to the floor. That distance is your inseam — enter it in centimetres.
- Measure twice and use the larger reading, since people tend to under-press the book on the first try.
What to do if you're between two sizes
The most common question in bike sizing is which way to round when you land between sizes. There is no universal answer, but a few rules settle most cases.
- Reach for the smaller frame if you want a sportier, more aggressive position or you have shorter arms — a smaller frame is easier to handle and lighter.
- Take the larger frame if you want a relaxed, upright position or you have a long torso, and you do not mind a slightly longer reach to the bars.
- Let standover height decide — you should be able to stand flat-footed over the top tube with a few centimetres of clearance (more on a mountain bike). If the bigger size fails that test, size down.
- Trust the test ride over the chart — a saddle, stem and seatpost can fine-tune fit within a size, but they cannot fix a frame that is two sizes wrong.
Brands also disagree on what "Medium" means, so a Medium in one make can match a Large in another. That is why this calculator gives you a frame number as well as a letter — the number ports between brands far better than the letter does.
Road vs mountain vs hybrid sizing
The same legs give a different frame size on each bike type, because each is designed for a different riding position and terrain. Here is how they differ and why.
| Bike type | Frame unit | From your inseam | Why it differs |
|---|---|---|---|
| Road | centimetres | inseam × 0.665 | Longer reach, lower standover for an efficient, stretched-out position |
| Mountain | inches | inseam(in) × 0.59 | Smaller frame, more standover clearance for rough, technical ground |
| Hybrid / city | centimetres | inseam × 0.64 | Between the two: upright comfort with enough reach for commuting |
A rider who takes a 56 cm road frame typically takes an 18–19 in mountain frame and a ~54 cm hybrid — different numbers, same legs.
Gravel and endurance road bikes sit close to road sizing; e-bikes and cruisers follow their hybrid or mountain base. When in doubt, size to the geometry chart of the specific model, since wheel size and frame design shift the fit too.
How accurate is this bike size calculator?
The math is exact for the inputs you give it. Inseam times the bike-type multiplier is the precise frame figure, and the inch conversion uses the exact 2.54 factor. If your inseam is right, the frame number is right to the decimal.
The recommendation is still a starting point, on purpose. Frame geometry varies between brands — reach, stack and top-tube length all move the real-world fit — so two 56 cm frames can feel a size apart. The height-to-inseam estimate also assumes average leg proportions. Measure your inseam, treat the result as the size to try first, and confirm it on a test ride or against the manufacturer's geometry chart before you buy.
Bike sizing definitions
Frequently asked questions about the free bike size calculator
About this Bike Size calculator
This bike size calculator runs entirely in your browser — nothing you enter is sent anywhere. It recommends a frame size from your height and optional inseam for road, mountain and hybrid bikes, applying the standard inseam-based fit formulas and returning both a frame number and the S/M/L letter brands print.
It is one of our transportation calculators; browse the full set on the calculators hub. Treat the result as a starting point and confirm fit against the model's geometry chart and a test ride before buying.