What Size Mountain Bike do I Need?

Use these tips to find the right size mountain bike based on sizing charts, standover height, and riding style.
What size mountain bike do I need

One of the most popular articles on Singletracks is an old one: Syd’s 2010 article titled, “How to Fit Yourself on a Mountain Bike Like a PRO.” In the article, he says starting with the correct mountain bike frame size is the most important thing you can do to get a great bike fit, yet many new riders find themselves asking the question: what size mountain bike do I need?

Purchasing a mountain bike is a big commitment, so it’s crucial that you determine what size you need before handing over your credit card.

Mountain bike frame sizes

photo: Greg Heil
photo: Greg Heil

First, buyers should note there is no standardization across mountain bike brands in terms of sizing. So, you might find a size medium Yeti frame fits you just fine, while on Niners you need a size large. In the past, bike companies attempted to standardize frame sizing by quoting bike sizes in inches, and this measurement generally referred to the seat tube length. Some companies, like Trek, continue to use this measurement on their mountain bike frames, but it’s no longer universally comparable.

Standover height

Standover height also used to be a decent way to measure bike sizing, with the idea being that when standing over a bike, there should be at least 1-inch of clearance between the top tube and the rider’s crotch. These days, however, most mountain bikes have ample standover height, no matter the size. Heck, Leah generally rides small or even extra small bikes, but there’s a good chance she can still stand over some of the extra large bikes I ride.

The sizing chart

Because mountain bike sizes vary so much from brand to brand, the best place to start is typically at the bike manufacturer’s website. It might take some sleuthing to find it, but most brands have a sizing chart on their website that recommends a frame size based on the rider’s height. This isn’t perfect since people with similar heights can have wildly dissimilar leg, torso, and arm measurements, but it’s a good place to start.

From trekbikes.com

Notice how the sizing chart above shows overlapping frame size recommendations for various rider heights. For example, if you’re 5’8″ (about 1.75 meters), it’s unclear whether you should get a 17.5″ frame or an 18.5″ frame. Looking at Niner’s size chart, we see a similar break at 5’8″ for their size small and medium bikes.

No matter what height you are, there’s a decent chance you’ll fall between frame sizes for at least one of the brands you’re considering–but don’t despair. This is actually a good thing because it means you have options in terms of choosing the size that best suits your riding style and body proportions.

Ok, so what if you are between sizes? Well generally, if you like to be “playful” on the bike and want a more nimble ride, go with the smaller size frame. On the other hand, if you’re looking for stability at speed or even improved climbing efficiency, opt for the larger size. Of course this is a pretty broad generalization, but unless you are prepared to geek out on frame geometry or body measurements, this should help point you in the right direction.

Try before you buy


Ok, so you’ve checked out the manufacturer’s website and have a rough idea of the frame size you need. Now, head down to your local bike shop or demo event and throw your leg over the bike!

Most bike shop employees should be able to help you confirm that you have selected the right size bike, and may be able to offer addition information to help you make your decision. Even a parking lot test ride can tell you a lot about how well the mountain bike fits you. If you feel unstable, chances are the frame is too big; if your quads are burning even with the seat post at maximum extension, the frame might be too small.

Some mountain bikers even consult with a professional bike fitter when selecting a new mountain bike, which generally has a cost associated with it, but it can save money in the long run if it means getting the right size bike the first time around.

Dialing in the fit to a T

Unless you’re ordering a fully custom mountain bike frame, chances are even if you find the right frame size, there will be some aspects of the bike that don’t fit exactly right. This is where Syd’s tips come in. For example, you can correct your reach by swapping the stem or adding an offset seat post.

If you already know your personal fit numbers (reach, handlebar and saddle height, etc.), this makes finding the perfect frame size much easier. So if you find you’re a size large in trail bikes from Pivot, Santa Cruz, and Specialized, chances are one of those bikes will be a better fit than the others based on your body type and ride preferences.

Choosing the right size mountain bike shouldn’t be too difficult, as long as you do a little research and consult your local bike shop for confirmation. Fortunately, even if you don’t get exactly the right size you need, there are plenty of after-market components available that are designed to help you get the best fit.