How to measure your Head Size:
First decide where you would like the hat to sit on your head, this is usually from the middle of the forehead, above the ears and around to the fullest part at the back of the head. Use a tape measure or piece of string and wrap around your head using these points as a guide (don't pull on the tape too tight).
If your head falls in between two sizes choose the larger size for comfort. Head size measurements usually range from 53cm to 58cm with the average being about 56 - 57cm.
Headsize 54 - 56 cm = Hat Size Small
Headsize 57 - 58 cm = Hat Size Medium