So how many litter boxes do you need? Data says that you should have as many litter boxes as you have cats. In this way none of your cats will be prevented from using the litter box if one of them is already occupied. It is also recommended that you place at least one litter box on each level of your house. Some cats do not like using a litter box after another cat has used it. Some breeds like long-haired cats seem to be pickier about using the litter box after other cats.
How many do I have? For many years I used one very large litter pan, actually it is a very large storage bin. For years it worked great for my multi-cat home. Though I have had some runabouts with my cats thinking “outside of the box” I have always been able to encourage them to go back to the large litter bin with success. When I got my present Siamese, she had litter box problems. I had to increase the number of litter boxes. She refused to share the litter box with my other cats and eliminated outside the box. Now I have three litter boxes, that I keep very clean. The Siamese is happy and now she relieves herself in the litter box.