USA
3 4 5 6 7 8 9 10 11 12 13
EURO
36 37 38 39 40 41 42 43 44 45 46
UK
3 4 5 6 7 7.5 8 9 10 11 12
CM
23 23.5 24 25 25.5 260 27 27.5 28 28.5 29
MM
230 235 240 250 255 260 270 275 280 285 290

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