This is the most common question we get asked.
If you are not sure of what your wheel size is, use the handy options below to find out:
Easy Option 1: Ask the bike seller
If you bought the bike online or from a shop, then check with the seller. The wheel size is probably listed in the specifications, or they can tell you.
Option 2: Check tyre markings
Most bikes tell you the wheel size right there on the tyre. If the information isn't online, this is the absolute best way of finding out.Wheel sizes have been measured in a variety of guides for some time now. At Swytch, we measure our wheel sizes by ETRTO number, a 5digit number of the form XXXXX which tells you the precise diameter. The most accurate way to determine your wheel size is by looking for markers on your tyres.
The first two digits of an ETRTO number specify the width in mm. Swytch wheels can take any width tyres from 1.12.5 inches (2864mm) so we do not need to know this. We are interested in the last three digits, which specify the tire inner diameter in mm. So if your wheel size is 32622, then it has width 32mm (inside our 2864mm range) and diameter 622, which is the 28” wheel.
Other than ETRTOs, wheel sizes can be written in inches, as Diameter x Width (for example, 28x1.75). The inch and mm diameters match up in the following way:
28”/700C/29er
The wheel sizes 28”, 700C and 29er or 29” all refer to the same rim size: ETRTO 622. The tyres can differ which makes it confusing, but the 28”, 700C and 29er are all the exact same rim diameter. The 700 marking will be followed by the width in mm, and the 28 or 29 marking will be followed by the width in inches. This is the most common wheel size, so look out for familiar markings (such as 28x1.75, 700x32C, 29x1.50).
Which 26” or 20” am I?
There are two 26” sizes, and two 20” sizes. For each of these, they are differentiated by their ETRTOs, or by the style in which they’re written.
The most common ones are the 26” (ETRTO 559) or the 20” (ETRTO 406). You can tell these because the widths are written as decimals, for example 26x2.00 or 20x1.50.
More rare are the 26” (ETRTO 590) or the 20” (ETRTO 451). You can tell these because the widths are written as fractions, for example 26x13/8 or 20x11/8.
Step by Step summary
 Look at your bicycle tyre for any markings. Look for a marking of the form XXXXX, where the last three digits corresponds to one of the ETRTOs in the left hand column in the above table.
 If you cannot see an ETRTO, look for a marking width x diameter, in inches. Find the width on the table and match it to the right ETRTO to pick your wheel size.
 If the diameter is 28, 700C or 29, this is your standard 622 wheel size.
 If the diameter marking is 26 or 20, check whether the width is in fractions or decimals and choose the ETRTO as above.
 If you’re still unsure, get in touch: www.swytchbike.com/hc/engb
Option 3: Measure yourself
A final option is to take off the bicycle wheel tyre, and measure the diameter of the rim, which is also called the ETRTO
Wheel Size  Rim Diameter / ETRTO  

622mm  
27" / 27.5" / 650C  584mm  
26" / 650C  559mm  
24"  507mm  
20" 451 (old style)  451mm  
20" 406  406mm  
16"  349mm 
Not sure? Contact us
Contact us and we can help you confirm your wheel size.