What size mountain bike is best for me?

A great fit goes a long way towards having a good time on the trail. Just like we don’t all wear the same size trousers, we don’t all ride the same-size frame. When you ride a bike that fits, you get more comfort and better control.

You may be used to choosing a bike size based on standover height or seat tube length. While those measurements are still worth considering, it’s more important to look at the Reach and Effective Top Tube measurements when comparing mountain bike sizes. You can find these measurements by scrolling to the geometry chart on each mountain bike’s detail page.

The easiest way to determine your frame size is by height, but many riders find that they are between sizes. Choosing to go up or down a size depends on your personal riding style and body proportions.

A bike with a longer reach will have a longer wheelbase. That makes it more stable, especially on high-speed descents. That’s great for riders who like to plough through rather than pop over rough stuff on the trail. If you have a relatively long torso or arms for your height, you may find that a longer reach gives you a roomier, more comfortable cockpit.

A bike with a shorter reach will have a shorter wheelbase. It’s not as stable, but it’s more nimble and easier to flick around. That’s great for riders with a more playful, active riding style who like to get off the ground and whip their wheels around. If you have a relatively short torso or arms for your height, you may find that a shorter reach makes it easier for you to hold the handlebars comfortably.

Effective top tube

Effective top tube is the horizontal distance from the centre of the head tube to the centre of the seat post. This measurement represents how a mountain bike fits while you’re sitting on the saddle. It’s important for cross country riders, who prioritise pedalling power.


Reach is the horizontal distance from the centre of the head tube to a vertical line that runs through the centre of the bottom bracket shell. This measurement represents how a mountain bike fits when you’re standing up on the pedals, like when you’re descending. Since most trail riders prioritise out-of-the-saddle riding, this tends to be the most helpful metric when comparing bike sizes from different brands.

The Trek Size Finder

This online tool helps determine the bike size that’s best for you. You’ll need a measuring device for your height and inside leg.

If you find that you’re between sizes, we recommend contacting your retailer or calling us on +1 800 585 8735 (M–F) for a quick consultation.

Expert advice from Trek

Online resources are great, but there’s nothing like a real person. You can connect with your local Trek retailer directly, call and chat online with us at Trek Headquarters.