Size conversion isn't an exact science. The numbers below are general, and come from a variety of sources. For sizes that depend on measurements, remember that one inch = 2.54 centemeters (although 2 1/2 is probably close enough to start).
US
UK
Europe
4
6
34
8
36
10
38
12
40
14
42
15
44
2 1/2
35
5
3 1/2
37
4 1/2
7
5 1/2
39
6 1/2
9
7 1/2
41
US General
US / UK
Small
87
Medium
91
97
Large
102
X-Large
107
112
46
117
US/UK
32
48
50
52
54
Men's Clothing Shoe Sizes
8 1/2
43
11
9 1/2
45
10 1/2
13
11 1/2
47
Men's Hats Hat Sizes
5 3/4
5 5/8
55
56
57
7 1/4
58
60