Cycling - Knowledge

Mountain Bike Sizing: An Easy Guide on How to Choose the Right Mountain Bike

1510 Views - 7 mins read

Mountains are dangerous terrains. Rugged surfaces, with boulders and gravels handing out the difficulty in walking let alone cycling on such rough exteriors. But there are certain members of the society that crave for an adrenaline rush. They look for dangerous risks to take on and relish the thrill that comes with them. One such thrilling sport is mountain biking. And if off-road cycling is “your thing” then to understand mountain bike sizing (for yourself) should be your priority!

Keep reading to find out how!

Purchasing a mountain bike from a store where you can check the comfortability in person is an excellent move. Plus, you get the expert guidance from the store representatives. But if online shopping is another one of “your thing” then we shall assist you in choosing the right mountain bike.

What Mountain Bike Do You Need?

Mountain Bikes
A Well-fitting Mountain Bike Will Render Comfortable Rides (source)

Fit is an important parameter to judge a mountain bike against. Riding a mountain bike that fits your body frame properly is very crucial. It will improve your handling and give you confidence on those challenging trails.

A mountain bike that’s small for your body frame will render discomfort while riding. You could suffer injury from long rides due to the cramped position. Then there are the potential toe overlap problems, wherein your foot clips the front wheel. Also, too much standover clearance can lead to back problems from longer rides.

Conversely, a mountain bike that’s too large for your body frame will not allow you to have a complete control on it. It can give you a sore back from overreaching on long rides and a lack of standover clearance can cause some wince-inducing accidents like hurting the crotch area.

So, you see how critical the fit of the mountain bike is! Now, how well a bike fits or feels on a trail is largely determined by the geometry of the bike frame. Let’s understand that before discussing the mountain bike sizing chart.

Mountain Bike Anatomy

Mountain Bike Anatomy
Anatomy of a Mountain Bike (source)

It is essential that you are well versed in mountain bike geometry if you are buying a bike online. A basic understanding of bike anatomy will be helpful while comparing bikes before you zero in on one.

The key mountain bike size indicators are:

1. Effective Top Tube (ETT)

Effective Top Tube of a mountain bike
Effective Top Tube Measurement (source)

This the traditional way to measure a bike length. Effective top tube is the horizontal distance between the head tube and the seat tube. The measurement is an important parameter to determine how well a mountain bike suits the rider when seated. The ETT measurement is governed by the bike’s seat tube angle and the rider’s saddle height. If you are planning to go on long rides, then focus on the effective top tube to understand the efficiency of the bike (how well a particular bike will handle) and how comfortably you can reach to grip the handlebars while seating.

2. Reach

Reach of a mountain bike
Reach Measurement (source)

The horizontal distance from the centre of the head tube to the vertical line that runs perpendicularly through the centre of the bottom bracket/crank is the reach of a mountain bike. If ETT determines bike efficacy and comfortability while seating, the reach measurement helps you to comprehend the same factors in standing position.

Most trail riders place emphasis on out-of-the-saddle riding. Hence, the reach measurement is a better guide then ETT to evaluate the efficiency of a bike.

Livingit Tip:
You can adjust the bike’s reach by swapping the bike’s stem.

3. Stack

Stack of a mountain bike
Stack Measurement (source)

Stack is the vertical distance from the centre bottom bracket/crank (of the frame) and the horizontal head tube line. The stack measurement affects your handlebar height and hand position which makes it a deciding element of comfort and control. Fortunately, you can easily adjust the stack measurement with headset spacers or simply by raising the handlebar.

4. Frame size

Frame size of a mountain bike
Frame Size is the Body of the Bike (source)

Mountain bikes come in all frame sizes to suit every rider’s body structure. If you know your height and inseam measurements then you can easily figure out the right mountain bike size for yourself. Also, of the two mentioned factors, inseam measurement is more important.

The difference between your inseam and the standover height should fall within the target ranges. (For example, if you have a 30” inseam, you’ll want a mountain bike with about a 28” standover height.)

5. Mountain Bike Standover Height

Standover height of a mountain bike
Standover Height Determines the Clearance Amount (source)

This is a traditional way to size a bike. Aside from the above-mentioned indicators, standover height can still be a useful determinant of whether or not a bike fits you.

First, ensure that you can straddle your bike with both feet flat on the ground. When you lift a mountain bike, a minimum clearance of 2" is required between the tires and the ground. That will allow you to comfortably get off the saddle for quick dismounts on the trail. Some (aggressive) riders seek 3" to 5" of clearance. Also, do the standover height evaluation with your cycling shoes as they may affect your overall leg length.

It is important to note that the clearance measurement is largely affected by the slope of the top tube going down towards the rear wheel. For example, if the slope gradient is extreme, then you are likely to have ample clearance irrespective of frame size. And thus, you cannot completely rely on standover clearance to determine if a bike fits. Hence the other indicators will have to be taken into account.

Mountain Bike Sizing Guide

Mountain Bike Size
Know the Right Mountain Bike Size for Your Body (source)

Before we present the ultimate mountain bike sizing guide, we believe that you should also learn how to measure your inseam. This will make the process of choosing the right mountain bike a lot easier. Many brands and manufacturers simply mark the bikes as S (small), M (medium), L (large), and sometimes XS (extra-small) and XL (extra-large) on either side of the bike for better distinction.

How to measure your inseam

You will need a large hardcover book (or notebook), measuring tape and a pencil. Next, put on your bike shoes and stand against the wall. With its spine up, straddle the book (as if you were sitting on a saddle). Using the pencil, mark the point at which the spine of the book touches the wall. Now, use the measuring tape to measure from the mark to the floor. This measurement is your inseam.

For accuracy, repeat the measurement a couple of times.

And now here’s the mountain bike sizing chart, check out!

Your Height

Your Inseam Length

Bike Frame Size

Descriptive Frame Size

4'11" - 5'3"

25” - 27”

13 - 15 inches


5'3" - 5'7"

27" - 29"

15 to 17 inches

Small - Medium

5'7" - 5'11"

29" - 31"

17 to 19 inches


5'11" - 6'2"

31" - 33"

19 to 21 inches


6'2" - 6'4"

33" - 35"

21 to 23 inches

XL - Extra Large

6'2" - 6'4"

35" and up

23 inches and up

XL - Extra Large


Some General Bike Shopping Tips

Here are some extra pointers to help you with the mountain bike sizing dilemma.

  • Your shining new bike should fit your current riding style. You can adjust its fit as you work on building your mountain biking skills.
  • Select the right frame size. If you don’t have the right frame from the beginning, you’ll face difficulty in getting accustomed to it in spite of all adjustments you make later.
  • Dialing the Fit to the T. Despite the right size, you’ll need to fine-tune the fit. Make simple adjustments to the bike’s components, such as seat height and seat angle. You can also swap the existing components.
  • And you can always go to a store and pick up some hands-on help from a skilled bike tech or sales associate. They will help in choosing the right size bike and/or personalize the fit.

Wrong Bike Size

Riding the wrong bike
Are You Riding the Correct Bike? (source)

Did I get my bike size wrong?

In such a case, you can tell the merchant, who can easily exchange the wrong bike for the right one. But if you do not want to do that, then you can follow the following procedures:

  • Adjust the bike’s saddle forwards or backwards
  • Get a longer or a shorter stem. It will alter your body position
  • Invest in a longer seat post

Sometimes the right bike might also feel wrong. And it is natural because it’s New! So, give it some time to get the feeling right. Practice on it regularly to get accustomed to the bulky body size. Mountain bikes are heavier than the regular road bikes.

There we have answered almost everything there is to know on mountain bike sizing. Hope that our guidance enables you to pick the right mountain bike without having to step into a store.

Mountain Bikes
You Need the Right Mountain Bike to Overcome Tricky Trails (source)

Fit and comfort are the deciding factors of most of the things we purchase. And in case of (mountain) bikes, they are the only factors that matter. In the absence of proper fit, which consequently offers comfort to the riders, there is the danger of injury and accidents, especially when you are paddling on the mountains. Your competency in controlling heavy cycles like the mountain bikes majorly depends on the fit. Therefore, a bike that fits well and is appropriate for your height, flexibility, and riding style is a bike that shall help you get the most of a riding experience.