To determine your hat size, have a friend help you with the following for best results. Sit upright in a chair, and with your friend standing up for a good view, they should measure the circumference around your head at the level of about 1”/ 2.5cm above the ears. Use a flexible plastic measuring tape, the type that can be purchased at any fabric or sewing supply store. The tape should go straight around the head, horizontal to the floor. Do not wrap the tape too tightly, and make sure the tape is on (not under) your occipital bone (the bump in the middle of the back of your head). The tape should be fitted to the head, but not constricting, and not loose enough to slip a finger between the tape and the head. You may want to measure more than once, to be sure that the measurement is accurate. Send us your head measurement in inches or centimeters.