What Size Mountain Bike Do I Need | Includes MTBs Size Chart

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Mountain biking is an epic sport and is personally one of my favorite disciplines when it comes to cycling. There are many things I love about it, from ripping down trails to relaxed rides with friends and even the odd race or XC event. It took me quite a few years to start enjoying mountain biking, and I made many mistakes along the way. One of the main mistakes I made when first starting was getting the wrong sized bike. This caused some of my riding to look pretty awful for others to see, and it also felt terrible. My body didn’t thank me for it, and I had to learn the hard way. In this article, I want to speak about getting the correct sized mountain bike for you, so you don’t make the same mistakes.

What Size Mountain Bike Do I Need

Why is it essential to have the right sized mountain bike

The majority of cyclists think getting the right size bike comes from having your saddle the correct height. If the bike seat post can adjust to the correct height, it is probably about right. This is a huge mistake to assume this, and it will cause your awful issues in the long run. Why it is essential to have the right size bike is a little more complex.

Mountain Bike Reach & Stack

Saddle Height

As mentioned before, if you don’t have the right size bike, you won’t achieve the correct saddle height. Not only this, but it’s important to have some room to play with if you choose to change your crank arm size, as this directly impacts the saddle height. If your saddle is too high, you will often feel pain in the back of your knees. If it is too low, the front and just under that cap is the most common place to feel discomfort. If you can’t adjust it to the correct height, it will be the wrong sized bike.


If you have a bike that is too big or small for you, then it will be challenging to get the correct reach. Reach is how far away the stem is from the front of the tip of the saddle. If the bike is too small, you will find yourself too upright and feeling compressed by the handlebars. If the bike is too big for you, it will feel too far away. Getting the incorrect reach will completely change how the bike controls and how it will feel.


Another very common issue we see with incorrect-sized mountain bikes is the Stack is not correct. The Stack height is the measurements from the bottom bracket shell to the tip of the saddle going vertically upwards. This is important as you need to be sitting just behind the bottom bracket so you can direct as much power into the pedals, and also, when seated, it will help with control. It’s not difficult to get right, as using different stems will help you adjust this. If the bike is the wrong size and you adjust it too much, it will change how the bike was designed to handle, and it might be unpleasant to ride.


I was lucky enough to get a bike fit qualification many years ago, and one of the most common issues I had was when people came to me with bikes they had bought off friends, and they were the completely wrong size. I often had to turn people away as the bikes were just too big or small for them.

How Mountain Bike Geometry Differs in Styles Mountain Biking

Another thing to note when getting the proper sized mountain bike for you is the geometry correct for what you intend the mountain bike for. The first thing you need to do is understand that unlike other bikes such as road bikes and gravel bikes, mountain bike geometry is much more complicated and has many other factors to it. There are four main types of mountain biking disciplines, and the bikes made for them have different geometry to suit. 

  • Cross Country: Made to go long distances of terrain, which is pretty light and not super technical. They are made to soak up light bumps and have a comfortable geometry and suspension travel up to about 130mm. Many mountain bikes in this discipline will be hardtails and only have front suspension.
  • All-Mountain: Very similar to Cross County because they are made to be comfortable on and go long distances. The difference between the two is these bikes will mainly be All-Mountain Bikes are typically full suspension, and they sometimes have up to 150mm travel for the bumps.
  • Enduro: Made for plenty of ups and down and super technical terrain. They are much more aggressive than All Mountain and Cross Country. They will typically be full suspension and have 170mm of travel. Enduro races are not the longest of races, and because of this, these bikes are made to be fast. The rider will be aerodynamic and be able to tackle rough terrain with ease.
  • Downhill: Not meant for long rides. They are super aggressive and made to get down a hill as quickly as possible. They will be full suspension, and travel on that suspension can be above 200mm. These bikes will not be comfortable to ride, and you will find them limiting if you were to try cross country on one.


Taking all this into account, it’s imperative to understand what style of bike you are buying. It is vital to get the size right. Also, the type of riding you plan to be doing is significant. I would find a long XC race challenging on a Downhill bike and feel I wouldn’t enjoy it at all.

Where to Start

When you first start looking at mountain bikes, you have a few different options about which way to go forward. Depending on how much you are looking to spend on a bike or what kind of riding you plan to do, I would be starting in different places. 

First Timer

If you are entirely new to Mountain Biking and are looking at bikes, I would first think about what discipline you want to ride and then start looking for bikes around that. Once you have found a bike that suits your needs, I would look at the manufacturer’s recommendations on what size you need and a general sizing chart. If the bike is second hand make sure it matches what you need. If it is new from a shop, see if they have that size in stock. When it arrives, get a bike fit.

Regular Rider

Being a regular rider, you will probably find yourself spending a lot more money on a bike. I personally, like the beginner, would follow the same process. Still, before you hit that buy now button, I’d personally be tempted to find a dealer and see if you can have a go on a demo bike or try riding something with very similar geometry. Even if you have a friend with one, it’s essential to see how it rides. I would highly recommend getting a bike fit after this too.


If you are an expert and looking to go semi-professional or highly competitive, I would take a completely different route. I would go to a bike fitter with a bike fit rig and get the fit before buying a bike. The Bike Fitter will give you the correct information you need to select the right bike for the discipline you plan to ride. Get the bike and then get it fitted by that fitter. You will be spending a lot of money on the bike and using it for quite a long time so make sure you get it right the first time.


Although these methods are pretty straightforward, it isn’t always the best way to go. Mountain bikes come in many different shapes and sizes, and different manufacturers recommend different sizes for different heights. This is why we always recommend trying a demo. As mentioned before, it’s a good idea to use a sizing chart too. In the next section, I want to introduce you to our general sizing chart.

Sizing Chart

A lot of riders find themselves using a rough sizing chart instead of the manufacturer’s guidelines. This comes in handy when custom building or generally if the manufacturer’s guidelines are not as helpful as intended after a demo. We also find this extremely useful when it comes to buying second-hand bikes too. Information on older bikes can get lost easily, and you can find yourself without the information you need to make the right choice of bike

Rider Height CmRecommended Frame SizeGeneral Frame Size
148cm to 158cm13” to 14”XS
159cm to 168cm15” to 16”S
169cm to 178cm17” to 18”M
179cm to 185cm19” to 20”L
186cm to 193cm21” to 22”XL
194cm +23” +XXL

So as you can see, taking your height will give you a recommended frame size. The frame size generally will suit that height. We have also added what most manufacturers display when it comes to their sizes.

What if I’m between sizes?

outdoor biker woman

Quite often, I find myself between sizes when looking at bikes. I am about 185cm personally and find myself between a Large and an Extra Large. This gets difficult, and you have to choose if you want to undersize or oversize the bike. This is a common practice for bike fitters, but one thing you will find from doing this yourself is that it can change the characteristics of how the bike will ride. Let’s use an example of someone who is between a medium and a large.


Let’s say we want to go up to using a large size. We will start by saying the bike will be slightly longer. This length will come all over the bike and will make the bike feel less agile on a small scale. Typically the less agile the bike feels, the more control the bike will have. This also means the reach between the saddle and the stem is going to be longer. This will mean the rider will have to stretch forward more and be in an aerodynamic position. This could be uncomfortable for the user if they don’t have the flexibility in the hips to do so. You can counter this by shortening the stem, but then your stack height might be incorrect. Generally, on a more oversized frame, your seat post will be lower, meaning the handlebars will feel higher.


Let’s say instead of going to a large size. We drop to a medium. This means the bike will be shorter and feel much more agile and nimble than the larger bike. The reach on a smaller bike will be much shorter, making the rider closer to the handlebars, this will force the rider into a more upright position, and they will find it comfortable, but it can feel cramped. With a more petite frame, your Seatpost will be higher in the frame, and the handlebars will feel much lower and more aggressive. 

A rule of thumb

Upsizing and downsizing are very complicated, but I generally have a rule of thumb that I recommend to friends and clients. If you have a short torso and long legs, downsize. If you have a long torso and shorter legs, upsize. 

Understanding Manufacturers Sizing

Manufacturers will use many different shapes and sizes, and it can be a complete minefield when it comes to buying a bike. You will find they all use different sizes to each other and even recommend different sizes for different heights. Try not to overthink it and use different methods and recommendations before picking a bike. First, I look at what the manufacturers recommend. Then I look at the sizing chart. Then, after all, that what I tend to do is always look at the reviews. I recently bought a bike and had to return it because the sizing wasn’t suitable for me even though I used the manufacturer’s recommendations and the sizing chart. After I went through the reviews and many other people had the same issue. If I had read the reviews before, it would have changed my opinion on what to buy. 

The Importance of having a Bike Fit 

When you get your bike and have had a couple of rides and realize you are happy with it, maybe it’s time to think about having a bike fit. I personally highly recommend it to anyone. A fitter will help you get into the perfect position, and this will have a considerable amount of advantages for your riding. It will help you have more control when riding. It will keep you much more comfortable on the longer rides and give you a much more direct power transfer.

Expert Tip

Your local bike shop will be an excellent resource when it comes to trying demo bikes and getting advice. Another good opportunity is renting bikes from bike parks as well. It will give you a good indication of whether the bike will work for you and if it is going to be a good investment for your cycling. Cycling technology is becoming incredible, and although impressive, it is getting costly. It’s always good to do your research and try a bike before you buy one.


When it comes to getting a bike-sized right for yourself. I would highly recommend using the manufacturer’s guidelines and always having a demo if it is possible. Suppose you are buying second-hand and don’t have that information. I would recommend using the sizing chart we have provided. Even after this, a bike fit would be really beneficial as well. Try not to rush into buying a bike, wait for the right one to come along, and don’t compromise on the sizing.

Frequently asked questions

What is the best Mountain Bike for doing everything?

In my opinion, I would go for a mountain bike which has light full suspension. This will be able to do a bit of everything and as a daily bike work excellently. It will be primarily suited to Cross Country and All Mountain but will be fun to use.

Can I Bike Fit myself?

Yes, you can. There are loads of applications on the market which you can film yourself on the turbo trainer and adjust according to what the application recommends. It’s a time-consuming process, and I would recommend a qualified fitter personally.

If I do have the wrong bike size, should I sell it?

I would recommend selling it or personally or taking it to a professional fitter to see if they might be able to get you close to the correct position for you. The best thing to do is not buy the wrong sized bike to start with.

What if the seat post doesn’t go low or high enough?

You can either look for other seat posts, but this indicates that the bike is more than likely the wrong size for the rider.

Robbie Ferri CPT

A Personal Trainer and Ultra Cyclist living in King's Lynn in Norfolk, UK. From Ultra Cycling World Records to Bikepacking Races and a huge amount of time on the gym floor training myself and clients my experience when it comes to Health and Fitness is vast.

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