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How Do You Measure a Mountain Bike Frame Size?

Have you ever wondered why despite a small frame size recommended for mountain bikes, some just feel too small? Or, you thought that the frame size was small enough, but still feel that the size feels big? This is the impact of not knowing the right mountain bike frame.

So, how do you measure a mountain bike frame size? We all agree that the mountain bike frame size is different from a road bike or the hybrid bike frame size. 

Anyway, What Size Mountain Bike Frame Do I Need? 

Finding the right frame size is not as difficult as it sounds, especially not today when everything is simplified. The better part is that there are different methods of ensuring that you get just the right mountain bike frame size for you.

Let’s get onto the intricate details of each of the methods:

1. Inseam Measurement

Inseam measurement means that you take the inner legs’ length, from top to bottom. 

You will stand with your legs slightly apart, then take the measurement from the floor you are stepping on to your crotch area., where the legs start.

Once you get the measurement, determine what type of mountain bike you want and the trail you want to ride on.

If you want a downhill mountain bike, take your inseam length and subtract 14 inches to the measurements. Since mountain bike measurements come in inches, it is best to take measurements in inches. Or, you can take the measurements in centimeters, then multiply the results by 0.3937 to convert them to inches.

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When taking a mountain bike for cross-country ventures, subtract 13 inches. When you do this, you will get the right mountain bike frame size for you.

However, the most recommended method when using the inseam to get general mountain bike measurement is this: your inseam measurement multiplied by 0.66.

To simplify the metrics for you, below is a bike frame size measurement versus different inseams;

Inseam (CM)

Mountain Bike Size (Inches)


15- 16


15- 16


15- 16


16- 17


16- 17


16- 17


17- 18


17- 18


18- 19


18- 19


20- 21


20- 21


20- 21


20- 21


20- 21



Does this chart make it simpler to gauge your inseam against the mountain bike frame size? Actually, the inseam is in cm, so you don’t have to make conversions. So, if riding downhill, you will take the sizing on the lower side, while riding a cross-country bike will take the higher side sizing.

2. Height 

You can also use your height to determine which mountain bike frame size suits you best.

How do you measure your height? Stand straight on the floor, preferably barefoot or in light socks. Using a tape measure, start measuring from the ground to the highest point of your head. The resulting number will give you your height.

This being said, your height determines your bike frame size to a large extent. So, mountain bikes come in six sizes, suitable for different height size ranges. In this case, the chart below will help us understand the different bike sizes for different heights.

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Height Vs. Bike Frame Size Chart

Height (Inches)

Frame  Size (Inches)

Frame Size

4’10- 5’1

14 and below


5’1- 5’5

15/ 16


5’5- 5’9

16/ 17


5’9- 6’0

17/ 18


6’0- 6’3

18/ 19


6’1- 6’6



Remember that the indicated measurements are just recommended. However, your exact bike size based on your height will depend on what trail you are on when on your bike. As with the inseam, you take a bike where your height ranges highest if you are on a cross-country trail, and vice versa for the hilly areas.

3. Measuring the Bike Frame Size

What if you already bought the bike but can’t tell the frame size? Or, you are getting the bike secondhand, and the seller doesn’t remember the frame’s size?

The bike size will always be present for the new bikes, usually just below the seat, by the seat post. However, if you don’t get yours or can’t understand the measurements used, here’s a simple way you can get your bike frame measurements.

So, get a tape measure, if possible, one that is in inches. Then, measure the seat length, usually starting under the seat post to the crank arm holding the bike’s pedals. If you are using a cm tape measure, convert the cm into inches by multiplying the result by 0.3937.

You will get the bicycle frame’s exact size since bike measurement refers to the seat post length.

Advantages of Getting the Right Mountain Bike Frame

You are probably wondering; does frame size matter when buying a mountain bike? I could go to a bike store and try riding in different sizes to see the most suitable.

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You can go to the store and pick the bike that offers you the best ride, but what if several do the same. After all, every bike feels great on a first ride or quite uncomfortable. Knowing what you want saves you from making the wrong decisions based on first impressions.

Moreover, you may want to purchase a bike online, which is much cheaper and convenient. You cannot purchase a bike online if you don’t know what sizes are best for you. Therefore, knowing the right bike frame size will help you in this instance.

But why the bike frame size? The right bike frame size keeps you comfortable when riding. It also protects your crotch area from hurting. Besides, if a mountain bike is large, controlling it over the rough off-road conditions will be difficult. 

Bottom Line

How do you measure a mountain bike frame size? I hope that you now have the answer you have been looking for. Now it is up to you to do the necessary: take the measure of your perfect bike frame for a more thrilling and satisfactory ride.

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