1. Use a tape measure (or a piece of string that you can measure later with a ruler).
2. Place the string or tape around your head about 1 cm above your ear, across the middle of your forehead, and ensure it wraps completely around your head.
3. Keep the tape snug but not too tight.
4. Measure exactly where the hat will sit on your head.
5. The final hat size corresponds to the circumference of your head in centimeters: if your measurement is between sizes, choose the larger size.