The answer to this question all depends upon how many cats you have. Generally, you should have at least one pan per cat and then have one extra- roughly breaking down into 1.5 per cat. Some owner says that you should have 2 for each, while others feel that it is overkill. One way to limit the number of pans that you need to buy is to opt for the extra large models that can fit up to 3 cats at one time. If you purchase large enough pans, you can get away with purchasing only one per cat in your household.