For proper fit and size measure the circumference of your head 1" above your eyebrows and around the largest portion of the back of your head.
20 5/8" - 21 1/4" ----------- X-Small
21 3/8" - 22" --------------- Small
22 1/8" - 22 7/8" ----------- Medium
23" - 23 3/4" --------------- Large
23 7/8" - 24 5/8" ----------- X-Large
24 3/4" - 25 3/8" ----------- XX-Large