specialized giant cube cannondale merida castelli endura altura
Hardtail mountain bike on trail

Mountain Bike Size Guide

Choose the right size MTB bike with our bike size guide. A good MTB fit will be more comfortable and easier to handle, as well as enabling you to ride more efficiently.

What size mountain bike do I need?

Getting the right mountain bike frame size will make all the difference to your riding. A good fit will mean you are more comfortable on the bike, the handling easier and you will be able to ride more efficiently. 

In this guide we will explain MTB sizing, show you how to use the size charts and bike size calculator so you can get the best mountain bike fit.

To get the right fit simply match your height and inside leg measurements to the frame size recommended by the manufacturer. Our handy bike size calculator makes this nice and easy.

Multiple mountain bikes in a line

How are mountain bikes sized?

Mountain bikes are either sized in inches or with a general size like small or medium. MTB's are sized by the frame and this is traditionally based on the length of the seat tube, measured from the centre of the front chain ring to the top of the seat tube. 

However, mountain bike frames don’t always follow a classical design so the measurement may be based on a virtual seat tube measurement. Sizes do vary slightly between manufacturers.

Measuring MTB for sizing

How do I choose the right mountain bike size?

To choose the right mountain bike size, measure your height and your inside leg (inseam) and then use our handy bike size calculator.

Measure your height

Take your shoes off and stand on a flat surface next to a wall with your legs together and shoulders back.

Place a pencil on your head holding it horizontally, make a little mark on the wall and measure the distance from there to the floor.

Measure from head to toe for MTB size

Typical Mountain Bike Sizing Chart

Frame Size

XXS - 13"




XS - 15"




S - 16"




M - 18"




L - 19"




XL - 20"




XXL - 21"




XXXL - 22"




What size MTB should I choose if I am between sizes?

Sometimes our bike sizing calculator will recommend two different sizing options. This means that both the larger and smaller sizes recommended will both be suitable. It is a personal choice which size to go for, but most mountain bikers tend to opt for the larger size. So you don’t feel too stretched, you can (depending on the model) fit a shorter stem to improve the fit of a larger bike without adversely affecting the handling. This is the opposite to a road bike where it is better to lengthen the stem rather than shorten it.

Kona Mountain Bike front end

For model specific sizing please check the product page.

Please note all sizing information is to be used as a guide only. This is because bike sizes can vary for different brands and models. If you are unsure which size bike will be best for you, our bike specialist team are here to help. Call us on 01792 3465601, chat with Live Help or email info@tredz.co.uk and we will be happy to assist you.

MTB sizing table(Click to expand)


Mountain bike size (Inch)

4’8” – 5’1”  |  143 – 155 cm

13” – XXS

5’1” – 5’4”  |  155 – 163 cm

15” – XS

5’4” – 5’7”  |  163 – 170 cm

16” – S

5’7” – 5’10”  |  170 – 178 cm

18” – M

5’10” – 6’0”  |  178 – 183 cm

19” – L

6’0” – 6’3”  |  183 – 191 cm

20” – XL

6’3” – 6’5”  |  191 – 196 cm

21” – XXL

6’5” – 6’9”  |  196 – 205 cm

22” – XXXL

26" wheels

26 inch MTB wheel size

This is the traditional mountain bike wheel size but most MTBs now feature larger wheels. 26” wheels are still a good option for junior riders and smaller adults who will find them more manageable than larger hoops. Most dirt jump MTBs still roll on 26” wheels.

27.5" (650b) wheels

27.5 inch or 650b MTB wheel size

This is now the most common wheel size on all mountain bikes from trail bikes to downhill steeds. 27.5” wheels offer the ideal balance between the nimble handling characteristics and rapid rolling performance. Some manufacturers offer 27.5” wheels on smaller sized models with 29” wheels for the larger frame sizes.

27.5"+ (6Fattie) wheels

27.5 inch or 6Fattie MTB wheel size

With 2.8” and 3.0” tyres on a 27.5” rim these tyres have a similar overall diameter to 29” wheels and are often compatible with 29er MTBs that feature BOOST axle spacing on the fork and back wheel. Offering more grip and more float (cushioning) this wheel size is ideal for hardtails although the extra weight will make them slower to accelerate.

29" wheels

29 inch MTB wheel size

29ers are becoming increasingly popular, especially with cross country, enduro and downhill racers. While slower to accelerate, these larger hoops carry speed much better over rough terrain so tend to be faster and offer more grip due to the larger contact patch of the tyre on the ground. They are less nimble than 27.5” wheels and some smaller riders will find them a bit of a handful in technical terrain.

Most Popular Mountain Bikes