Find a string or cloth measuring tape. The goal is to measure where you would usually have a hat sit.
Looking in a mirror, start at the center of your forehead an inch above your eyebrows. Gently wrap the string or cloth tape around your head, a finger width distance above your ears, to the most prominent point in the back of your head. Meet at the starting location in the center of your forehead.
Mark the joint. If you are using a string, measure the start and end points in centimeters for most accurate measurements. We recommend measuring three times for accuracy.