The sizes indicated on the socks correspond to Italian sizes. Here is the correspondence of the sizes:

Shoes Europe 39 40 41 42 43 44 45 46 47
Shoes UK 5.5 6 7 8 9 10 10.5 11 11.5
Shoes USA 6.5 7.5 8 9 10.5 11 11.5 12 13

 If you hesitate between two sizes, prefer the smallest size.