There are several sizes of fishing hooks, the most common ranging from 1/2 to 3 inches in total length. The gape, or space between the barb and the shank, is typically half the length of the shank.
There is no international standard for measuring fishing hooks, so every manufacturer may have slightly different sizing. Fishing hooks are generally classified according to a numbered sizing guide. The appropriate size hook to use depends on the size and type of fish. A size 4 hook, which is about 1.8 inches in total length, is an appropriate hook for a number of freshwater fish, such as carp, channel catfish and smallmouth bass.