Centimeters 49.5 50.5 52 to 53 54 to 55 56 to 57 58 to 59 60 to 61 62 to 63
Inches 19 ½ 19 7/8 20 ¼ to 20¾ 21 to 21 5/8 21 ¾ to 22 ½ 22 5/8 to 23 ¼ 23 ½ to 24 24 1/8 to 24 ½
XS
(xs and smaller is for kids)
S M L XL 2XL 3XL
6 ¼ 6 3/8 6 ½ to 6 5/8 6 ¾ to 6 7/8 7 to 7 1/8 7 ¼ to 7 3/8 7 ½ to 7 5/8 7 ¾ to 7 7/8 8

OSFM = one size fits most
Measure 1 inch above the ears and to the tip of the forehead

 

HOW TO MEASURE YOUR HEAD

Head Measurement

Measure around your head making sure the tape passes across the Centre of the forehead, above the ears and over the natural bump at the back of the head.
Don't have a measurement tape? Use a string around head, then measure it on a ruler.