S: 55 - 56 cm
M: 57 - 58 cm
L: 59 - 60 cm
XL: 61 - 62 cm
Place string or tape around your head (normally 1 cm above the eyebrows and ears).
Hold it comfortably, not too tight, as you would like your hat to fit: most sizing errors happen by applying the band too tightly. If your measurement is between sizes, choose the next larger size.