USA
6M 7M 8M 8.5M 9M 10M 11M 12M
EURO
36 37 38 39 40 41 42 43 44 45
UK
3 4 5 6 7 7.5 8 9 10 11
CM
23 23.5 24 25 25.5 26 27 27.5 28 28.5

If you normally wear a ½ size, buy the next full size. For example, 10 ½ , buy an 11.