The right frame size makes a bike feel natural: you can reach the bars without stretching, stand over the top tube without discomfort, and set the saddle at a height that protects your knees. A frame that is a size too large or too small is a common reason people stop enjoying cycling. This calculator takes your height and looks up the frame size from a published chart, for road bikes (in centimetres) and mountain bikes (in inches and S/M/L).
How to use the bike size calculator
- Measure your height without shoes, standing against a wall, in centimetres, inches or feet.
- Choose the bike type. Road bikes are labelled in centimetres; mountain bikes in inches or with S, M, L labels.
- Read the frame size and the band of rider heights it covers. If your height sits at the edge of a band, look at the next frame size too.
- Check the brand’s own geometry chart and, if you can, test ride.
Bike size formula: how the lookup works
lower height limit included, upper limit belongs to the next frame
There is no formula that works for every bike; manufacturers publish tables. The table below is the BikeRadar bike size guide (retrieved 2026-10-15). The feet-and-inches column is calculated from the centimetre limits by dividing by 2.54 and rounding to the nearest inch.
| Rider height | Height (ft/in, approx.) | Road frame | Mountain frame |
|---|---|---|---|
| 143–155 cm | 4′8″ – 5′1″ | 44 cm | 13 in |
| 155–163 cm | 5′1″ – 5′4″ | 48 cm | 15 in |
| 163–170 cm | 5′4″ – 5′7″ | 51 cm | 16 in |
| 170–178 cm | 5′7″ – 5′10″ | 54 cm | 18 in |
| 178–183 cm | 5′10″ – 6′0″ | 56 cm | 19 in |
| 183–191 cm | 6′0″ – 6′3″ | 58 cm | 20 in |
| 191–196 cm | 6′3″ – 6′5″ | 60 cm | 21 in |
| 196–205 cm | 6′5″ – 6′9″ | 62 cm | 22 in |
BikeRadar also gives a T-shirt-style table for mountain bikes, which is what the “S/M/L” result uses:
| Mountain bike size | Frame size | Rider height |
|---|---|---|
| Extra-small | 13–14 in | 152–162 cm |
| Small | 14–16 in | 162–170 cm |
| Medium | 16–18 in | 170–178 cm |
| Large | 18–20 in | 178–185 cm |
| Extra-large | 20–22 in | 185 cm and over |
Worked example
A rider is 175 cm tall (5 ft 9 in) and wants a road bike.
- 175 cm lies in the 170–178 cm band, so the frame is 54 cm.
- For a mountain bike the same band gives 18 in, and the T-shirt table puts 175 cm in Medium.
- At 178 cm exactly the rider would move into the next band: 56 cm road or 19 in mountain.
What else matters besides height
- Inseam (leg length): standover clearance depends on the legs, not the height. If your legs are short or long for your height, trust the standover test; see the Inseam Calculator.
- Reach and riding position: a racing position stretches you further forward than an upright commuter position on the same frame.
- Bike type: gravel, endurance and race bikes use different geometry even at the same labelled size.
- Brand: there is no standard between manufacturers, so a 54 from one maker can ride like a 56 from another.
When you are close to a boundary, ask a shop to check the fit on the exact model. A saddle and stem change can fine-tune a frame that is nearly right, but they cannot fix a frame that is the wrong size. This page is a starting point and not a bike fit.
Sources
Every figure above comes from these pages, read directly on the dates shown.
- BikeRadar — Bike size guide: how to find the right size bike — checked 2026-10-15
- Giant — STP bike sizing guide (reference for fit advice) — checked 2026-10-15
Frequently asked questions
What size bike do I need for my height?
Match your height to a frame size on a chart. On the BikeRadar table a rider of 175 cm needs a 54 cm road frame or an 18 inch mountain frame. This calculator does the lookup for you and shows the height band the frame covers.
Is the frame size the same as the seat tube length?
It used to be. Many road frames are still labelled in centimetres, but modern frames with sloping top tubes are labelled by effective size, and mountain bike brands mostly use S, M and L. Always check the brand’s own geometry table for the exact bike.
What if I am between two sizes?
Brands differ on advice. Giant says a smaller frame is more agile and a larger one more stable. A bike shop can check standover height, reach and saddle position. Test riding both is the best way to settle it.
Do road and mountain bike sizes match?
No. Mountain frames are smaller for the same rider, which is why the calculator gives centimetres for road and inches for mountain. Do not use a road size to buy a mountain bike. Related: Inseam Calculator.
Why does the frame size not fit even though the chart says so?
Charts are built around average body proportions. Arm and leg length vary, and so do riding position and bike type, so the chart gives a starting point rather than a final answer.