A bike frame measurement is important, especially when you’re buying or selling a bike, or trying to figure out how tall a person should be to ride it. You get the frame size by measuring the appropriate part of the bike, depending on what type of bike it is. If the bike is measured incorrectly, the rider could end up with an improper fit, resulting in poor posture, discomfort, and even pain for the rider. This guide will help you measure your bike correctly. You can navigate using the links below:
Bike Measurement Tool
For detailed instructions and diagrams on measuring a specific type of bike, try our online bike measurement tool. It shows you exactly what to measure for your bike and provides a chart of suitable riders for each bike size. This information is useful when selling a bike, since many casual buyers will simply want to know whether the bike will fit them or not.
You can also click any of the applicable bikes on this page for more information about measuring that type of bike.
Common Bike Measurements
There are a handful of ways that bike frames are measured. We explain the simplest and most popular ones below.
Center to Top (C-T)
This refers to the length of the seat tube, from the base to the top. The base is the round section at the bottom holding the axle (known as the bottom bracket) and the top is where the seat post goes into the seat tube.
Center to Center (C-C)
This is similar to the C-T measurement except the top of the seat tube is defined by the intersection of the center of the top tube and center of the seat tube. This measurement is more common among European manufacturers.
Applicable bikes: Road
Top Tube (TT)
This is the length of the top tube, which is the main connecting tube between the seat tube and head tube (at the front of the bike). It is measured from the centers of the intersecting tubes.
Applicable bikes: BMX
Wheel Diameter (D)
This is calculated based on the diameter of the wheel or, more simply, the tire size. Bikes measured this way have frames designed relative to the size of tire, so the larger the tire, the larger the frame.
Applicable bikes: Cruisers, Kids
Some bikes use a simple overall bike measurement such as small, medium, large, x-large or even one-size-fits-all. This is possible since the bikes have a more casual upright riding position and are easily adjustable to accommodate a larger range of riders within each bike size. The bike size is usually on a sticker somewhere on the frame.
Applicable bikes: Folding, Electric
Measuring Wheel Size
Most bikes use one of these three sizes of wheels: 26”, 27” (older bikes), and 700C (or 29”). Knowing your bike’s wheel size is helpful when you’re looking to replace tubes or ties and when selling your bike, since buyers may be interested in knowing this information. Find the tire size of your bike by looking on the existing tire or the wheel rim. The first number will be the diameter and the second number is the width of the tire.
Example tire size: 26” x 2”
If you don’t have the old tire or can’t find the tire size on the rim, you can measure the rim yourself. The easiest way to do this is measure the circumference of the rim around the bead seat. The tire bead is the innermost portion of the tire that sits within the rim, on the bead seat. Using a soft measure tape, like the ones used by a tailor, wrap it around therim along the bead seat (or as close as you can get). This is the bead seat circumference. Convert it to millimeters (25.4mm = 1 inch) and find the measurement in the table below:
|1954mm||700C or 29″|
Keep in mind, this wheel measurement applies to both the tire and tube.
To learn more about rim sizing, and for less common sizes, visit Sheldon Brown’s Rim Sizing page.
Measuring Crank Size (L)
While most bikes ship with standard crank sizes, it’s helpful to know the length of your cranks, especially if you’re selling the bike online. You measure the cranks, in millimeters (mm), from the center of the holes at each end of the crank.
Visiting Your Local Bike Shop
When in doubt, you can always take your bike down to the local bike shop for a measurement. They can tell you the size of the frame, cranks and wheels, and may even give you an idea of what the bike is worth.