There are 2 main categories for hook size:

Small hooks: They have numbers such as #1, #2, #4, #6, #8, etc. The larger the number, the smaller the hook. For example, a #10 hook is much smaller than a #2.

Large hooks (with "aught" - /0): These have numbers such as 1/0, 2/0, 3/0, 4/0, etc. The larger the number before the "/0", the larger the hook. For example, a 5/0 hook is larger than a 1/0.