What size mountain bike do I need?

Ask an experienced rider about bike fit and they’ll tell you that all bikes feel and ride differently, even if their numbers look almost the same on paper.

Manufacturers’ listed mountain bike frame sizes can be confusing. The traditional method is to list the seat tube length, but even that varies because some are measured to the top of the seat tube and some to the middle of where the top tube joins the seat tube.

Many manufacturers simply list their bikes as S, M and L, perhaps with XS or XL at either end.

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And, more recently, bike manufacturers have begun listing their bikes’ sizes based on reach figures rather than seat tube and top tube lengths.

This means they’ve been able to grow the bike’s reach figure, wheelbase and top tube length while trying to keep seat tube lengths and stack heights shorter and lower.

Smaller seat tube lengths mean that shorter people can fit on bikes with a longer reach figure because they can adjust the seat height lower, opening up the potential to ride a larger bike.

But it’s still important to consider seat tube and top tube length when buying a bike. The seat tube length will dictate the lowest saddle height that can be set and the top tube length will roughly dictate how stretched out a rider will feel.

So, where do you find out what size frame you need? Like so many other things on a mountain bike, there is no one perfect solution because within sensible limits you can adjust your saddle, stem and handlebar to help make a slightly imperfect fit feel fine.

We’d always recommend looking at manufacturers’ own size charts, which will usually list a suggested height range for each bike frame size they produce, but here are some general guidelines:

Bike size

Frame size

Rider height

Extra-small

13 – 14in

152cm – 162cm (5ft – 5ft 4in)

Small

14 – 16in

162cm – 170cm (5ft 4in – 5ft 7in)

Medium

16 – 18in

170cm – 178cm (5ft 7in – 5ft 10in)

Large

18 – 20in

178cm – 185cm (5ft 10in – 6ft 1in)

Extra-large

20 – 22in

185cm plus (6ft 1in plus)

(Bear in mind that road, cyclocross and hybrid bike sizes tend to be 3 to 4in bigger for riders of the same height – something that confuses a lot of riders when looking through bike listings. Read our guide to road bike sizes for more information.) Gook luck, hope you find the right mtb just for you.