Bike Frame Size Calculator
Bike frame size and starting saddle height from your inseam, for road, mountain and hybrid bikes.
Stand in socks against a wall with a book pulled up into your crotch and measure floor to book: that is your inseam.
How the bike frame size calculator works
Stand in socks against a wall with a book pulled up into your crotch and measure floor to book: that is your inseam. Road frames run about 0.665 × inseam in centimetres, hybrids 0.685, and mountain bikes 0.226 × inseam in inches. Saddle height (bottom bracket centre to saddle top) starts at 0.883 × inseam — the LeMond method — and is fine-tuned from there. Manufacturers size differently, so treat the result as the size to try first.
Formula: road frame = 0.665 × inseam; hybrid = 0.685 × inseam; MTB (in) = 0.226 × inseam(cm); saddle = 0.883 × inseam
Worked examples
| Inputs | Frame size | Note |
|---|---|---|
| 84 cm inseam, road bike | 55.9 | 55.9 cm |
| 84 cm inseam, mountain bike | 19 | 19.0 in |
| 33 in inseam, hybrid | 57.4 | 57.4 cm |
FAQFrequently asked questions
Do I measure inseam with shoes on?
No — barefoot or in socks, standing straight against a wall with a book pulled firmly up into the crotch. Your trouser inseam is shorter and gives the wrong answer.
Why are mountain bikes sized in inches and road bikes in centimetres?
Convention: road frames were measured along the seat tube in centimetres, mountain bikes in inches, and many brands now use S/M/L instead. The calculator gives all three.
What if I fall between two sizes?
Go smaller if you like a nimble, more upright position or have a short torso; larger if you have a long torso or want a stretched, stable ride. A test ride settles it — reach matters as much as height.
How do I set the saddle height from here?
Set the distance from the centre of the bottom bracket to the top of the saddle at 0.883 × inseam, then adjust a few millimetres either way until your knee is slightly bent at the bottom of the pedal stroke.
Where these figures come from
- World Handicap System — Rules of Handicapping — the score differential and handicap index formula
- International Cricket Council — Playing Conditions — over structure and run-rate definitions
- Cricket Australia — the national body for the sport these statistics most often describe here
Last checked: September 2026. Formulas follow the governing bodies where one publishes them — the World Handicap System for golf, the ICC playing conditions for cricket run rates.