The number of litter boxes you should have in your home depends on two factors: First – the number of cats that you have and Second, the size of your home.
The rule of thumb is you should have at least one litter box per cat plus one OR one per floor, which ever is more. So if you live in a two-story home with 3 cats – you should have 4 boxes. If you live in a three-story home with one cat, you should have three boxes.
This may seem like a lot but the recommendation is intended to minimize inappropriate urination in the house, a common behavioral problem in cats.
For more tips on caring for your cat's litter box, please read The Fine Art of Litter Box Care