I decided to answer this b/c nobody else was (I say this becasue I'm not an expert at all). It's one inch of fish per 1 gallon.
There is a table for it, it's something like:
1 inch fish (tail not included) = 1 gallon of water
2 inch fish (tail not included) = 3 gallons
3 inch fish (tail not included) = 8 gallons
I, personally, got stuch with a three-inch iridescent shark, four inch goldfish (tail not included), two platies, and an algae etaer, in a five gallon tank! They've been there for over four months (though I had eighteen fish in there at the beginning b/c I had no idea what I was doing, and all but three died
(that's when I bought a handbook on it)) and only one platy died (not of the top two) but that, I believe, was because I had to move it to a net breeder and back.
In short, it all depends on the size of your fish, gallons per # of inches, and where the fish normally swims. (I.e. danios at top, platies in middle, corydoras, plecties, and algae at bottom, and goldfish everywhere)
Sorry if this made me seem as though I was insinuating that you were a novice (I, myself, am a novice by the way), but I just wanted to get that info out.
Whew.
Hope that helped.