Size Matters: How to Measure a Bike Frame Accurately

Bike with a white frame

Knowing how to measure a bike frame is essential for many reasons. If you are buying a new bike, then understanding how to measure a bike frame will ensure that you are buying the right size bike. If you are adjusting the seat or handlebar on your bike, then measuring the bike frame accurately will make sure that you have a safe and comfortable ride. In learning how to measure a bike frame, we will go over what the bike frame really is, when you should measure the bike frame, and finally guide you through how to measure a bike frame yourself.

Let's get to measuring so you can get to riding!

What Is a Bike Frame?

Blue bike frame near a wall

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First things first, the bike frame is the aluminum skeleton of the entire bike. A bike frame is essentially the backbone of a bike, which connects all parts of the bike to a central point. The bike frame gives the bike shape, supports the seating, holds the wheels and pedals, and also connects to the handlebars. Clearly, picking the right bike frame is important. Otherwise, everything else about the bike will be wrong.

How Are Bikes Measured?

Bikes are measured according to frame size and bicycle type. Some styles of bikes, like mountain bikes, are smaller in general than other bikes, such as cruisers. However, regardless of the style of bike, all bikes define frame size by the length of the seat tube, not necessarily by the height of the bike itself.

Most bikes are measured in inches for a matter of simplicity, but depending on the brand and the place where you purchase a bike, you might be looking at measurements in centimeters. Always know the measurement of your bike frame in both centimeters and inches, for the sake of simplicity when looking for parts or when making repairs.

What Is The Seat Tube?

The seat tube is the main vertical part of the frame that supports the seat and seat post. If you are looking at a bike, then the seat tube is the part that is between your legs, connecting the seat to the rest of the bike. Bike frames are designed in such a way that the rider perches on the seat tube while riding, which means that a seat tube that is too long or too short for your height will put you in an awkward place to steer to the bike.

When Do You Need to Measure a Bike Frame?

Most people measure a bike frame when they are in the process of purchasing a bike. This is the best time to measure a bike since you don't want to buy a bike that is wrong for you. You might also measure a bike when you are buying a bicycle for someone else, like a child. Knowing your bike's measurements also comes in handy when you need to adjust different parts of your bike when you need to purchase new wheels or rims, and even when you buy certain bike decals.

Why Should You Measure A Bike Frame?

Red bike frame

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First and foremost, having the right measurement for your bike frame means having a comfortable bike riding experience. If you aren't comfortable on your bike because the frame is wrong, then you will end up riding less or not riding at all, which defeats the purpose of having a bike. Measuring a bike frame also comes down to the safety and control you have while on the bike. The wrong size frame can lead to crashing your bike or injuring yourself.

How to Measure A Bike Frame

Choosing a bicycle with the right fit makes riding more comfortable and give you better control. There's nothing worse than peddling a bike and having your knees ram up against the handlebars, or having to stretch for the handlebars because the bike is too large. Learning how to measure a bike frame will prevent both of these problems. Here are the steps in how to measure a bike frame:

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It's fairly easy to learn how to measure a bike frame. The entire process takes maybe one or two minutes at most. If you aren't certain that you've done the measurement right, you can always go into a bike shop and get a professional fit. The shop will measure you on a bike and give a recommendation of the bike sizes you should be looking at when shopping for a new bicycle.

Guidelines For Meas​​​uring Bike Frames

Sometimes, the final answer to sizing a bike doesn't only involve the bike frame size. Sometimes, you need to look for other factors to make sure that the bike frame you choose will give you the most comfortable riding experience. There are three things to look for while you are physically sitting on the bike you are thinking of purchasing.

Guideline One: When the bike pedal is at its lowest point, your foot should be flat on the pedal when your leg is fully extended. If your knee is bent, then the bike is too small for you. If you have to use your toes to reach the pedal, then the bike is too large for you.
Guideline Two: When the pedal is at its highest point, your knee should not come above the horizontal bar on the frame connecting the seat to the handlebar. If your knee is too high, then the bike is too small.
Guideline Three: When the bike is upright, see if you can touch the ground with your toe. If your toes can't touch the ground, then the bike is too large.

The seat position can always be adjusted if you need to tweak how extended your leg is or if you are just barely able to touch the ground. However, if adjusting the seat position does not solve any of these problems, then you are likely trying out a bike that really is the wrong frame for you. Being comfortable in any position on the bike is important to make sure that you are able to operate the bike to your fullest ability.

Basic Height Requirements

Sometimes, accurate measurements of a bike frame are a little less helpful than we want them to be since not all manufacturers use the same measurement rules. However, there is no such thing as being too tall or too short for bike riding. However, when searching for the bike frame that is the right size for you, there are general rules that can help you find the right frame more quickly.

18 Inch Bikes: These are mid-size bikes that are usually good fits for people who are between 5 feet 8 inches tall and 6 feet tall.
16 Inch Bikes: These are smaller size bikes that usually work well for people who are 5 feet 7 inches or shorter.
20 Inch Bikes: These are larger size bikes that are typically best for taller people, such as those who are over 6 feet tall.

Conclusion

Black bike near a white wall

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It is quick and easy to learn how to measure a bike frame. By identifying the seat tube, you can easily take the measure of any bike frame and find a bike frame that is right for you. While all sizes of bikes vary according to bike style, you can still use the general length of the seat tube to find the frame that is right for you.

Average height people do well on 18-inch bikes, shorter people do well on 16-inch bikes, and taller people do well on 20-inch bikes. There are a few guidelines you can use while trying a bike out to make sure that you have selected the right size bike frame for your height. In general, some adjustment to the seat position will make sure that you have a comfortable fit on a bike. There are professional fits available at most bike shops to make these adjustments for you.

Knowing how to measure a bike frame is important to make sure that you have a safe and comfortable biking experience. Riding a bike in the wrong size can be a safety hazard and can make riding the bike outright uncomfortable. The better the bike frame fits your height, the better your ride will be since you will have more control over the bike.

In the end, knowing how to measure a bike frame is an unavoidable aspect of purchasing a bike—but it truly pays off, in the end, to be riding a bike in the right frame. For bike frames, size truly matters.

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