How to Measure Bike Frame Size

How To Measure Bike Frame Size

If you are going to purchase a new bike or sell one that has been lying in your yard, you’ll have to know its frame size. Measuring a bicycle before purchasing one will help you get a bicycle that suits your physique and allows you to ride easily.

Do you struggle to measure a bike frame size since you don’t understand where to begin? Finding the appropriate size bike can be simple, but it can also be a big challenge. Much of this is due to the fact that not all bicycle companies measure or display their frame measurements the same way.

It is excellent practice to understand how to measure a bike frame. It’s useful if you’re planning to upgrade your bicycle. This article will explain how to measure the bike frame size in simple steps.

Anatomy of a bike

Here’s a general view of a bike so that you can easily understand how to measure bike frame size.

Now we will discuss the procedures. Let’s dive in to know how to measure bike frame size.

Top Tube Length Measurement

To begin, check for the size tag on the lowest part of the seat tube. A seat tube is a pretty long tube to which the bicycle seat post is attached. A glued-on label indicating the bicycle’s frame size may be found towards the bottom of the seat tube, around 3 inches up from the chain sprocket.

Although not every bike frame has a size label, it will save your time and effort if yours has. If the size is not mentioned, you must physically measure the seat tube. Remember that the frame size can be provided in either inches or centimeters.

When there is no labeling, start measuring from the middle of the gear crank to the upper end of the seat tube. Set the tip of a measuring tape at the exact middle point of the gear crank. Now, bring the measuring tape all the way up to the upper end of the seat tube. Measure all the way to the end of the seat tube. It’ll tell you the seat tube length, and that’s the bike frame size.

You can take the saddle from the top of the seat tube and keep it aside if this assists you measure. The seat tube length on most standard-sized bikes is between 21 and 23 inches (53 and 58 cm).

If you’re measuring a road bike, change the measured values to centimeters. If you live in the United States, you are most likely used to working with imperial measures. Road bike frame sizes, on the other hand, are usually stated in centimeters. To get the length in cm, multiply the value by 2.54. Assume the seat tube’s length is 22-inch. Multiply this number by 2.54 to get 56.5 cm. If you are dealing with a frame of a mountain bike, stick to inches.

Related: How to Measure Bike Wheel size?

Choosing the Right Size Bike

Keeping your legs open, measure from the floor to the groin. Stand on the floor with your legs wide open, barefoot. Spread your feet widely so that they are 6–8 inches wide. Measure the distance in cm between the floor and your groin with your measuring tape.

Confirm that you are measuring to your actual groin, not the groin of your jeans. Whether you feel it difficult to calculate this distance on your body without collapsing, request a good friend or colleague if they would be glad to help.

If you are looking for a road bike, multiply the inseam length by 0.7. You will have a difficult time riding a bicycle if the seat tube is almost the same length as that of your inseam length! If you are going to use a road bicycle, multiply the inseam length by 0.7.

Road bicycles are an excellent choice if you want to do most of your riding on paved routes. Assume your inseam length is 65 cm. When you multiply the leg inseam by 0.7, you get 45.5. You’ll get a total of 46 if you round up your results.

If you want a mountain bicycle, multiply the inseam length by 0.66. Mountain bikes feature bigger, heavier tires than road bicycles so that you will be quite high from the ground. To adjust, multiply your inseam length by a little lesser figure to determine your proper bike size. If you do not even enjoy doing mathematics in your brain, get a calculator.

MTB bicycles are your ideal option if you will be riding mostly off-road or through steep hills. Assume your inseam length is 76 cm long. Multiply the inseam length by 0.66 to obtain a reasonable estimate of 50.

Buy a bicycle having a frame size that matches the value you measured. The number you get from the formula you just calculated refers to the size of the bicycle that will suit your physique. However, it’s a good idea to check by riding a bicycle before purchasing to ensure that it’s suitable. Set the seat such that your legs are bent at a quite modest angle while fully stretched and pressing down on the pedals.

Measuring Other Tubes

In millimeters, measure the length of the vertical head tube. The head tube links the handlebars to the upper end of the fork of a bike frame. Place the tip of your measuring tape on the upper edge of the head tube where it meets the handlebars. Measure by going down to the forks of the head tube, taking your measurement.

Be careful to exclude the handlebar post’s base from this measurement! The head tube is the smallest of the basic bicycle tubes. As a result, head tube lengths are often provided in millimeters, although many other measurements are normally provided in centimeters.

Measure the effective top tube to account for a tilted top tube. As the name implies, the top tube extends almost parallel to the floor, from the seat post to the head tube. When you estimate the length of a tilted top tube, you’re basically calculating the “effective top tube.”

Place one end of a level at the intersection of the top and head tubes. Keep the level straight and take a record of where it crosses the seat tube. It’ll most probably be just a few inches above the point where the actual top tube meets the seat tube.

The top tube length of the bicycle frame should be measured. Set the end of a measuring tape on the head tube’s middle point, where it crosses the top tube. Calculate the length in cm by measuring all along the top tube to the midpoint of the seat tube. If you have a tilted top tube, evaluate the effective top tube position that you already measured and noted. The entire distance is the length of the top tube.


Search for a size labeling on the base of the seat tube before manually measuring the bicycle frame’s size. Many bicycles have the frame size marked directly on the frame. If there is no labeling, simply measure from the middle of the gear cranks to the upper end of the seat tube. The frame size is determined by the measurement you take. Calculate in inches when you are sizing MTB. If you are sizing a road bike, use centimeters instead of inches. We hope this article has cleared how to measure the bike frame size!

Jeffrey Kuck

Meet Jeffrey Kuch, a passionate cyclist who has been cycling for more than a decade. With his love for the sport and his unwavering dedication, Jeffrey has not only honed his skills but has also inspired many to take up cycling. As an avid blogger, he shares his insights, experiences, and knowledge about the world of cycling, helping fellow cyclists to improve their techniques and learn more about the sport they love. Whether he is exploring new terrains or competing in races, Jeffrey's enthusiasm for cycling is contagious. Through his writing, he hopes to inspire others to embark on their own cycling journey and discover the joy of the sport.

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