Sized Hat sizes
CM Inches US size

48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68

18 7/8
19 1/4
19 5/8
20   
20 7/16
20 13/16
21 3/4
21 5/8
22
22 3/8
22 3/4
23 1/8
23 1/2
24
24 3/8
24 3/4
25 1/8
25 1/2
25 15/16
26 5/16
26 5/8

 6
6-1/8
6-1/4
6-3/8
6-1/2
6-5/8
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
8
8-1/8
8-1/4
8-3/8
8-1/2
S/M is Small to Medium (Size 6 to 6 ½ approx)
L/XL is Large to Extra Large (6⅝  to 7½ approx)

FM is One Size fits Most; if you have a small head, this may be too large for ladies. If you have an extra large head, over 7¼, this may be too tight.