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What Size Mountain Bike Frame Do I Need?

Now you’re looking for a bike, but you don’t know what size MTB frame you need for your height?

Buying your bike is the biggest riding-related investment you’re going to make, so you want to get it right the first time round.

This 2-minute guide covers everything you need to know.

How To Measure A Mountain Bike Frame

If you’re buying second hand, there’s a good chance the owner doesn’t know the exact frame size. In fact, even newer bikes are sometimes labelled in sizes that don’t relate to a specific size in inches (i.e. medium).

So, you’re going to need to know how to measure a mountain bike frame.

Grab yourself tape measure and take the measurement from the top of the seat tube, to the center of the bottom bracket (the bottom bracket is what your crank arms connect to).

Mountain Bike Frame Size Chart

Now you’ve got this measurement, you’re ready to pick out the right size frame.

Height Frame Size Frame Size In Inches
5ft – 5ft 2” 13” – 14” Extra Small
5ft 3” – 5ft 5” 15” – 16” Small
5ft 6” – 5ft 9” 17” – 18” Medium
5ft 10” – 6ft 1” 19” – 20” Large
6ft 2” – 6ft 4” 21” – 22” Extra Large
6ft 5” and above 23” – 24” Extra Extra Large


That size chart is a guideline, and it’s always worth referring to manufacturers own frame sizing charts.

Some will vary slightly (i.e. an extra small might be 13.5-14.5”) and some manufacturers measure differently (i.e. from the center of the BB to the bottom of the seat tube, rather than the top).

In-Seam MTB Frame Sizing

To be 100% sure on bike sizing, you’ll need to go and test some out.

One person that’s 5ft might have an in-seam of 25” whereas another might be 27”. And that’s going to completely change up the frame size you’ll need.

You’ll need to go one size up on the frame size, but potentially use a shorter handlebar stem so you’re not overstretching when you’re on the trails.

What Happens If Your Mountain Bike Frame Is Too Small?

If you get a MTB frame that’s sized too small, you’ll get:

  • Cramp in your knees
  • Back and neck pain
  • Bruises on your knees from hitting them off the handlebars
  • Lack of stability at higher speeds

What Happens If Your Mountain Bike Frame Is Too Big?

On the flip-side, you definitely don’t want a frame size that’s too big. Frames that are too big will lead to:

  • Excess frame weight for no reason
  • Lack of stability at lower speeds
  • Back pain from overstretching to reach the bars and control the bike

Essentially, it’s better to have a frame at the larger end of the spectrum, than the small end.

However, you want your MTB to have the perfect frame size – this is especially important if you want to improve quickly, or are planning long XC rides or trails.

What’s Next?

Thanks for reading our 2-minute guide to mountain bike frame sizing.

Got any questions? Leave a comment and we’ll get back to you.

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Grant's a motorcycle geek, outdoor enthusiast & confirmed racing nut. He road tests all the gear he buys, and then gives his feedback here on NoobNorm. He also details any quick fixes he stumbles upon, whether that's to stop brakes on motorcycles sticking, or unusual noises coming from gaming wheels.