Hooked on Numbers...

I've noticed that many new anglers are always intimidated by the myrid array of fishing hooks with weird sizing numbering system... There is no clear history on how the current hook sizing came into existence. The measurements used today use a twofold numbering scheme that measures from the smallest hook to the largest hook. It depends on what species of fish your are targetting for. It also depends on the condition of the water and how the fishes are feeding at that moment.

Here's a chart showing you the measurement scale of the common bait hooks and recommendation based on species. (click for larger version)

Also there is a very useful sizing chart for those who wants to build their own lure.