it will depend on the maximum growth of the fish you’re going to get. for a 12 gal tank, you shouldn’t purchase any fishes that exceeds 3” fully grown. you can probably put around 5 fishes that grows to be 3”, probably a dozen or so if the fishes only grow to be 1.5”. i own a 10gal with 4 cory catfishes, which grows out to be around 3” and 7 neon tetras, which grows to be 1.5” and they’re living nicely.
also make sure that you don’t mix south american/african, semi-aggressive fishes, community fishes in the same tank, i did that in my 29 gal tank and all hell broke loose, i had headless fishes floating every morning til i eventually had to buy a 10 gal tank.

10 – 17 med/large fish ought do the trick
dependes what size fish ur gettin
if there really small u can have like 50 in a tank
with out a problem

1in of fish = 1gal of water This method is good for normal aquariums 35yr exp

It really depends on the size of the fish, the dwelling levels of the fish and also waste output. Why don’t you have a look around the internet, find some fish you like and then try to work out a stocking list around that? is a good place to look for pictures of fish.

When you’ve worked out a stocking list, or you’ve found a couple of fish you think you’d like to have, feel free to email me and I can help you add or take away from your list.

Don’t follow the inch-per-gallon rule, it is rather outdated and generally does not work.