How to Size a Mountain Bike

Thinking of buying your new mountain bike online? You'll need to know what size bike to buy, so check out this handy explainer.

It can seem dangerous to buy a mountain bike from the internet, as you won’t get a chance to try the bike out until it comes in the mail. Though you can often find a better deal online and have more options to choose from, some people are still wary. Luckily, it is still very possible to get the right size bike when ordering on the web, meaning we can still use the increased supply and options that the internet has brought us. I have bought bikes online myself (including my first mountain bike years ago) and helped many people find the perfect bikes for their size as a cycling expert here at Curated. All it takes to find the perfect fitting new bike is a couple of quick measurements and the knowledge of how to apply them.

The information in this guide will work for any adult. Sizing bikes for both men and women follows the same process, though women may want to take a few extra things into account. They should consider the width of their shoulders, which might make a typical mountain bike’s handlebars feel too wide. Bikes sized specifically for women use narrower handlebars (and other small tweaks) to better accommodate this potential difference. Regardless, most women still feel perfectly comfortable on Unisex or Men’s bikes, and a women’s-specific bike is never completely necessary. The idea that women must ride women’s bikes is a total myth.

A woman on a mountain bike smiles at the camera

Key Measurements

Now, for sizing. To find the right sized bike, you will just need two important measurements. The first is one that you probably already have — your height. This is the most common sizing option, used by most sizing charts you will see, and works fairly well. Most manufacturers will go off of this measurement as well, as using height allows the bike to fit a rider overall, from seat height to reach.

Still, it is usually best to also use your inseam size to find the right fit, as this measurement can help ensure that a rider with slightly different leg lengths, torso lengths, and arm proportions will still find the best fit. For example, it will help to ensure that someone who has proportionally longer legs won't end up with a bike that is too cramped. It is an easy measurement to take, so there really isn't any reason not to use it. Note that this is a different inseam measurement than the one used by clothing manufacturers. If you try to use your pants length, you will end up with the wrong sized bike.

To take the measurement of your inseam, stand against a wall and place a book between your legs, positioning it to rest as a bike seat would. Then, have someone measure from the ground to the top of the book with a tape measure. This measurement, which will be the length of your inside leg can then be used in conjunction with your height to more accurately size a bike.

A mountain biker makes their way down a rocky path
Photo by Tobias Bjerknes

Using a Size Chart

Now, with measurements in hand, look at the recommended size chart listed by the seller or the manufacturer, or a general sizing chart (which you can find by googling “Mountain Bike Sizing Chart”). With any of these charts (from a trusted source - don’t go off an internet Q and A site), you will be able to see where you land on mountain bike frame sizes.

Reading the charts is easy. On one side will be listed heights, inseam lengths, or both, and on the other the correct frame size (listed in inches, as opposed to the metric system used for road bike frame sizing) for the measurements. Your height and inseam length will probably match with a range of frame sizes. If they don’t — say the chart lists a 19” bike for your height but an 18” bike for your inseam — you will know that you have proportionally shorter legs. If this occurs, go with the frame size based on your inseam length over your height — a bike that is too small for your height will be much less comfortable than a bike that fits your inseam.

Most charts will include a range of sizes that will work for your height or inseam. Go for a larger frame in your size range if you want a more aggressive, leaned-over riding position, and go for a smaller one if you would prefer to be seated more upright. You can now take the frame size you pick and go back to the bike you are considering. The description should list the size of the frame, or will allow you to select a size if there are multiple options. This size is standardized, based around the clearance the rider will have when standing over the top tube with both feet on the ground. It is important to use this size, because other measurements aren’t necessarily standardized — for example, there can be variation in how top tube length is measured depending on the manufacturer and geometry of the bike.

A cyclist wearing blue shoes and a blue jacket rides along a dirt road
Photo by Markus Spiske

Other Considerations

A few other considerations you might want to make when sizing your bike. For one, wheel size - if you are under 5'5", you will want to go with a bike that has 27.5-inch wheels (the smaller size for mountain bike wheels), as 29ers will probably be too large. Someone who is over 6'4", on the other hand, will want to go with 29-inch wheels, for the opposite reason. Next, don't worry about the length of the seat tube, as this is the most easily adjustable dimension on a bike, and won’t change the fit of the bike much.

Once you choose the correct frame size, you will be all set to order your bike. Soon you will be ripping over dirt with a comfortable ride! Add it to the cart resting easy that you will have picked the right bike for your size. If you still aren’t certain you will be able to find the right fit, your Curated expert is always there to help with any specific sizing questions you have.

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Written By
I started mountain biking with my father when I was twelve. He took me out on my cheap bike and I struggled to keep up with him for hours. It was a hot summer day. I was exhausted and barely made it back to the car. I couldnt walk without groaning for days. Still, I loved it, and have loved it ever...

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