Is there a certain way to tell the hook size if you don't have anything to compare them too? I have a terminal tackle box with a few hooks that I just really don't know what size they are.

some manufactures have charts on their websites where if you print the picture on an 8.5x11 the pictures of the hooks will be actual size so you could use that

All though you'll see charts there aint really any standards

Some have short shanks, some have longer shanks, & then there's punch hooks that look like a gaff!

I pay more attention to the gape, the distance from the point to the shank.

You could also take them to a tackle shop and compare them or they should be able to tell you the size (depending on which tackle shop and person you talk too)

After buying hooks I take them out of the package and put them in one of  two small plano's, one for straight shanks and the other for ewg's (forget the plano model #)  then I just match them up to the size bait Im going to use,...

 Probably have about 150 to 200 or more hooks in each plano, and no reference to what size they are anymore, just match them to the plastic, by sight. From a 3" grub, to a 12" worm, I have whatever worm hook I need, in them.

 The plano's are about 7 inches long, and 3 inches wide,and maybe a inch tall,... and have a possible 9 compartments when all the dividers are in, which I have done. And these fit in many of their boxes/bags nicely.