All you need to do is measure from the center of the wheel hub to the rim’s outside edge and double the measurement to get the total diameter of the wheel. Then, compare that number to our chart at the beginning of this article and you’ll find out what wheel size you’re dealing with. Note that you need to measure the diameter in millimeters.

Prop your bike against a wall, or mount it on a bike stand. This will allow you to accurately measure your bike’s wheels without it falling over. Measure from the ground to the wheel’s axle in inches. This will give you the wheel’s radius, which is half of its diameter. It’s best to use a retractable tape measure so you have a free hand.

With the bike in a steady position, put a tape measure against the core of the wheels. After that, extend the tape tightly and straight towards the tire’s inner edge as required by the ISO standards. However, the reading you’ll get is the radius. Therefore, you should multiply the number by 2 to get its diameter.