The easiest way to determine what size inline wheels your skates use is to simply look at the wheels that are currently installed. Usually you'll find two numbers printed on the wheels that indicate the size and the durometer. The size will be stated in millimeters with a number followed by 'mm' (example: 80mm). The durometer can be similar a number, but followed by the letter 'a' (example: 80a). Although the number 80 is used in both examples the 'mm' and the 'a' after the numbers indicates they're different pieces of information. The more important number to know about your inline wheels is the size in millimeters.