Bike Size Calculator
Estimate your road and mountain bike frame size and starting saddle height from inseam and height.
About the Bike Size Calculator
Frame size is mostly about leg length and reach. Common starting points: road frame (seat tube, cm) ≈ inseam × 0.70; mountain bike frame (inches) ≈ inseam (cm) × 0.226; saddle height ≈ inseam × 0.883 from the centre of the crank (Greg LeMond's method). Brands measure frames differently and many now size by S/M/L, so check the maker's chart and test ride.
The formula
Road = inseam × 0.70 cm; MTB = inseam (cm) × 0.226 in; saddle = inseam × 0.883
Worked example
Example: Road frame size = 62 cm
- Inputs: Units: inches; Inseam (crotch to floor, in socks): 35; Height: 76.
- Formula: Road = inseam × 0.70 cm; MTB = inseam (cm) × 0.226 in; saddle = inseam × 0.883
- Result: Road frame size = 62 cm
- Road (inseam × 0.70): 62.2 cm
- Mountain bike (inseam × 0.226): 20.1 in
- Letter size by height: XL
Questions people ask
How do I measure inseam?
Stand against a wall with a book pressed up between your legs; measure from its top edge to the floor.
Between sizes?
Smaller frames feel nimbler; larger ones more stable. Try both.