Another useful thing to have here. These vary a little based on personal preference, but this is a close guide. Sorry about the formatting, hope it is readable.

mm | inch | hook size
------------------------------
1.5 1/16 24-20
2 5/64 18
2.5 3/32 16
3 7/64 16-14
3.5 1/8 14-12
4 5/32 12-10
4.6 3/16 10-8