How to choose your frame size

A frame that fits is the difference between a bike you ride and a bike you own. Stem, saddle and bars can all be swapped; the frame is the one part you cannot adjust. Here is how we size riders, step by step.

Start with two numbers

Measure your height and your inner leg length (inseam), barefoot. Our size calculator turns them into a frame size for road, gravel, MTB, e-bike and TT, and the size guide shows the usual ranges for each.

1. Stand against a wall, heels together, feet about 15 cm apart.
2. Pull a hardback book up between your legs, spine up, as firmly as a saddle would sit.
3. Measure from the floor to the top of the book. Do it twice and keep the average.

Inseam matters more than height: two riders of the same height can have legs several centimetres apart, and that changes the saddle height, the standover and often the right size.

How sizes are written

• Road and gravel frames are usually sized in centimetres (51, 54, 56…), roughly the length of the seat tube. A few brands use letters (S, M, L).
• Mountain bikes and e-bikes mostly use letters (S, M, L, XL); some brands still quote the seat tube in inches.
• The number is a label, not a standard: one brand's 54 can ride like another's 56. That is why the next step matters.

Read the geometry: stack and reach

Every brand publishes a geometry table. Two figures tell you most of what you need:

• Stack: how high the top of the head tube is above the bottom bracket. More stack, a taller, more upright front end.
• Reach: how far forward it is. More reach, a longer, more stretched position.

If you already have a bike that fits, compare its stack and reach with the new one. Within about 1 cm of each, the new bike will feel familiar; the stem and spacers do the rest.

Between two sizes?

• Pick the smaller frame for a lively, aggressive position, quick handling and a lighter bike. You can add a longer stem.
• Pick the larger one for long days, a more upright back and more stability at speed. You can fit a shorter stem.
• On a mountain bike, longer reach gives stability downhill; shorter reach makes the bike easier to throw around. Ride style decides more than height.

Stem length and saddle height adjust a lot. Frame size is the one thing you cannot change.

Buying used? Check the size first

A great deal on the wrong size is not a deal. Each used bike we list is one bike in one size, shown on its page, so check it against the calculator before you fall for the colour. If you are unsure, send us your height and inseam and we will tell you what we would ride.

Quick checklist

• Height and inseam measured, barefoot.
• Calculator result noted for the kind of bike you want.
• Stack and reach compared with a bike that already fits you.
• Between sizes: decide by how you ride, not by the number.

Ready to look? Start with road bikes, gravel bikes or the used bikes, and filter by your size.