Not all hats are available in all sizes. 
Please cross-reference styles that you are interested in ordering to this chart. Thank you.

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SMALL
MEDIUM
LARGE
X-LARGE
METRIC
54
55
56
57
58
59
60
61
62
63
U.S.
6 3/4
6 7/8
7
7 1/8
7 1/4
7 3/8
7 1/2
7 5/8
7 3/4
7 7/8
INCHES
21 1/2"
21 5/8"
22 1/8"
22 1/2"
23"
23 3/8"
23 3/4"
24 1/2"
25"
25 3/8"
Measurements given are for the inside of the of hatband of the finished hat which is the part
that touches the head.  Using a tape measure, begin measuring at the center of the forehead
just above the eyebrows and ears and continue around the head to the center of the forehead again. 
YOUTH SIZES
SMALL
MEDIUM
LARGE
X-LARGE
#1600, 1601
6 3/8
6 5/8
6 7/8
7
INCHES
20 5/8"
21 1/8"
21 5/8"
22 1/8"
Sizes are approximate