Bike size calculator
Choose the type of bike and enter your height and inseam. The calculator applies the rules of thumb fitters and shops often start from: a frame size from the inseam, a letter size from the height and a saddle height to begin with. Makers measure frames differently, so use it to narrow the choice, then check the maker's own chart and ride the bike.
Runs in your browser: nothing you enter is sent anywhere.
How to use
- Choose road, mountain or hybrid.
- Pick centimeters or inches and enter your height.
- Measure your inseam barefoot (see the FAQ) and enter it.
- Read the frame size in both units, the letter size your height usually falls into, and a saddle height to begin with.
How it works
The frame size comes from the inseam, because leg length decides whether you can stand over the bike and reach the pedals:
- road: inseam × 0.665, in cm (center of the crank to the top of the seat tube);
- mountain: inseam in cm × 0.226, in inches;
- hybrid / city: inseam in cm × 0.25, in inches.
The letter size comes from height bands: for road bikes S from 160 cm, M from 168, L from 176, XL from 184 and XXL from 192 cm; for mountain and hybrid bikes S from 155, M from 165, L from 178, XL from 186 and XXL from 195 cm. Saddle height = inseam × 0.883. All of these are common rules of thumb, not any maker’s chart.
Example
A rider 69 in tall with a 32 in inseam looks at road bikes. 32 in is 81.28 cm:
- frame: 81.28 × 0.665 = 54 cm, or 21.3 in;
- height 69 in = 175.3 cm falls in the road band from 168 to 176 cm: M;
- saddle height: 32 × 0.883 = 28.3 in from the center of the crank.
Tips
- Measure the inseam twice and take the larger value; a soft book or a measurement over shoes gives too short a number.
- Raise or lower the saddle in small steps from the starting height: at the bottom of the stroke the knee should still be slightly bent.
- For children’s bikes sizes go by wheel diameter, and these adult rules do not apply.
Frequently asked questions
How do I measure my inseam?
Stand barefoot with your back to a wall and your feet about 15 cm (6 in) apart. Push a hardback book up between your legs, spine up, as a saddle would sit, and measure from the floor to the top of the book. That number is more useful for bike sizing than the inseam of your trousers.
Which formula does the calculator use?
Common rules of thumb: road frame = inseam × 0.665 in centimeters, mountain bike frame = inseam (cm) × 0.226 in inches, hybrid or city frame = inseam (cm) × 0.25 in inches. Saddle height from the center of the crank to the top of the saddle = inseam × 0.883. These are starting points, not a manufacturer's chart.
Why do frame sizes differ between brands?
Makers measure the seat tube to different points, use sloping top tubes and label sizes their own way, so a 54 from one maker can fit like a 52 or 56 from another. Reach and stack, the horizontal and vertical distances to the top of the head tube, compare bikes better than the seat-tube number.
I am between two sizes. Which should I choose?
Riders with long legs for their height, or who want a more upright position, often go for the larger size; riders with a long torso or who like a lively, compact bike often choose the smaller one. Saddle height, stem length and handlebar width can fine-tune either, but a test ride settles it.