SIZE – Small fits for 55-56CM 21.6-22; Medium fits for 56-58CM 22-22.8; Large fits for 58-60CM 22.8-23.6. With an adjustable tape built in sweatband to help find the best fit. FOLDABLE: packable, crushable, NO crease! Great for cruise, travel, gardening, boating or beach vacation. UPF 50+ ,3.7 wide brim could block most sun UV rays. DETACHABLE CHIN STRAP: adjustable for a snug fit; won’t blown off when it gets windy. VENTILATED: perfect for beach vacation, also great for summer rides, fishing and hiking.