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.
20.8" - 21.3" ---------- X-Small
21.6" - 22.0" ---------- Small
22.4" - 22.8" ---------- Medium
23.2" - 23.6" ---------- Large
24.0" - 24.4" ---------- X-Large
24.8" - 25.2" ---------- XX-Large
25.6" - 26.0" ---------- XXX-Large
26.3" - 26.7" ---------- XXXX-Large