Hat Size.
To get your size and measure around your head above the ears where the hat sits and measure in centimetres. Do not do it too tight nice a relaxed will do it.
cm UK
Small 54 - 55 6 5/8 - 6 3/4
Medium 56 - 57 6 7/8 - 7 7 - 7 1/8
Large 58 - 59 7 1/8 - 7 1/4
X Large 60 - 61 7 3/8 - 7 1/2
XX Large 62 - 63 7 5/8 - 7 3/4