Bike frame size calculator
This bike frame size calculator works from your inseam: at 82 cm a trekking bike takes a frame of about 54 cm and a mountain bike one of just under 47 cm. Includes inches and common size steps.
Example: Inseam 82 · Unit: Centimetres · Bike type: Trekking, city and touring bike → Frame height: Frame height 54.1 cm (21.3 in). Source: Wikipedia – Fahrradrahmen (frame size: 0.66 / 0.69 / 0.61 / 0.57 of the inseam, usual size ranges, size increments). Updated: .
How it is calculated
The classic rule of thumb gets frame height from the inseam: trekking, city and touring bikes 0.66, road bikes 0.69 (plus up to 4 cm), cyclocross bikes 0.61 and mountain bikes 0.57 times the inseam. The frame is measured from the centre of the bottom bracket to the top of the seat tube.
Size steps and types
Common frame sizes run from 47 to 68 cm for trekking bikes, 41 to 61 cm for cyclocross bikes and 35 to 58 cm for mountain bikes. Classic frames come in 2 cm steps, mountain bikes mostly in 2 inch steps, which is about 5 cm. The calculator names the nearest common step for the frame height.
What the calculation cannot do
Modern frames often have a sloping top tube, so seat tube lengths are no longer comparable. Many makers therefore give sizes such as S, M, L or XL and a range of body heights, and the effective top tube length matters more. When test riding, set the saddle height first: with the leg stretched at the bottom of the pedal stroke the heel should just touch the pedal.
- Children’s bikes are chosen by wheel size in inches, not by frame height.
- On road bikes with a horizontal top tube, frame height is often one size larger than on a mountain bike.
Frequently asked questions
How do I work out my bike frame size?
Inseam times 0.66 for trekking and city bikes, 0.69 for road bikes, 0.61 for cyclocross bikes and 0.57 for mountain bikes. At 82 cm that is 54 cm for a trekking bike.
How do I measure my inseam?
Stand barefoot with a straight back, clamp a book between your legs and measure from the top edge of the book to the floor.
Does frame height work for bikes with a sloping top tube?
Only as a guide. For such frames the effective top tube length counts, which makers often sum up as S to XL.
Sources and legal basis
- Wikipedia – Fahrradrahmen (frame size: 0.66 / 0.69 / 0.61 / 0.57 of the inseam, usual size ranges, size increments)
- Wikipedia – Bicycle frame (frame size and fit)
As of: · Editorial policy
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