The sizes are mixed and correspond to the head measurement:
S = 56 cm - 22 in
M = 58 cm - 22.8 in
(recommended standard size for a gift)
L = 60 cm - 23.6 in
The head circumference is to measure around the widest part of your head. If your measurement falls between two sizes, choose the next largest size. Example: for 59 cm, choose L (60 cm).