Training / Bike fit
Bike Size Calculator: Frame Size and Saddle Height from Your Inseam
Find your bike frame size from your inseam: road and gravel frames in centimetres, mountain bike frames in inches, and a starting saddle height with the LeMond formula, with how to measure your inseam properly.
Bike Size Calculator: Frame Size and Saddle Height from Your Inseam: Three long-standing rules of thumb turn an inseam into sizes: a road frame's seat tube is about 0.665 × inseam, a mountain bike frame in inches is the inseam in centimetres × 0.226, and the saddle sits about 0.883 × inseam above the centre of the crank, Greg LeMond's formula. An 80 cm inseam gives a 53 cm road frame, an 18-inch mountain bike, and a 70.6 cm saddle height. Runs 100% locally in your browser with zero server file uploads.
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Stand barefoot against a wall with a book pressed up between your legs, spine against the wall, and measure from the floor to the top of the book: that is your inseam. Road frame = inseam × 0.665; mountain bike frame in inches = inseam in cm × 0.226; saddle height = inseam × 0.883, the LeMond formula. These are starting points: brands measure frames differently and many sell sizes as S, M, and L, so compare with the brand's own chart, and a test ride or fitting beats any formula.
Measuring the inseam
Stand barefoot against a wall, push a hardback book up between your legs as a saddle would, and measure from the floor to its top edge. Take the average of two or three tries.
Frame measurements
Road frames are usually given as seat tube length in centimetres, and mountain bikes in inches. Brands measure to different points, so the same number can fit differently.
How to use it
- Measure your inseam barefoot, with a book pressed up between your legs.
- Enter it in centimetres or inches.
- Read the frame sizes and saddle height, then compare with the brand's chart.
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Frequently asked questions
Why inseam rather than height?
Two people of the same height can have legs several centimetres apart in length, and it is the legs that decide standover and saddle height.
My brand sizes bikes as S, M, and L. What now?
Look up the seat tube length or the rider-height range for each size in the brand's geometry chart and pick the one nearest the result here; between two sizes, the smaller is easier to adjust.
Is the saddle height exact?
It is a starting point. Adjust in small steps so your knee stays slightly bent at the bottom of the pedal stroke and your hips do not rock.
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