Molly, different people have different rules, it's all relative really, if you are doing regular or less than regular tank maintenance and your water is testing fine every time, I'd say chances are you are understocked-fully stocked, if you have to do your tank maintenance too often, you either have puffers, goldies, something similarly messy, or you might be overstocked. I tend to use the 1" per gallon rule as a base figure and then work around it by the type of fish... for instance, my mom has a 70gallon I am trying to fill, since there are no really messy fish (tetras, otos, kuhlis, etc...) and it's a fairly large tank, I went a little over 1" per gallon, I have a 75gallon tank, but I have puffers, so I am leaning towards a quite low stock level (right now I have probably 14" of fish in there, the 3 f-8s, 2 dwarf platties, and 4 BB gobys, although I do plan on adding a few more of this or that).