How many tetras can live in a 2.5 gallon tank?

I don't know the size of painted tetras, but I have a 5-gallon tank with 3 neon tetras, 3 platys, 2 zebra danios, and 2 of something else(?). They range in size from about an inch (tetras) to a little over 2", and I've had them for months. Of course, the pet stores tell me the ratio should be 1" of fish per gallon which would allow for, at most, 5 neon tetras. I've always had more fish and they've done well. My tank has a different shape (15"↕, 21"↔, but only 3-1/4" depth). Don't know if that makes any difference. I also have rocks, plants, filter, etc. Good luck to her!