Continued from another thread:
Check the link below, and refer to the shank length and hook gap. To me everything is relative to a TMC 100 (the standard) hook. So, for example a TMC 921, which I use for most of my dries smaller than 16, is a 2X short 1X Wide hook. So, I translate that into a #16 TMC 921 has a shank length of a #20 (2 sizes smaller) and a hook gap of a #14 (1 size larger). I know it is not exact, but it works 90% of the time. I have a notecard with TMC 100 from #10 thru #24 lined up on it. I determine what size TMC 100 hook best matches the body of the fly I want to imitate, then I tailor my hook selection based on that shank length but also considering what the hook is designed for. So, if I want to tie a #20 BWO, I will typically use a #16 TMC 921 since it gives me the same shank length as a TMC 100. Hope this wasn't too confusing. It is the system I use, and it works for me. However, I don't expect it to work for everybody.