I have 17 cats and 4 litterboxes, but they are various sizes of plaste crates. One of them is over 10 gal...easy. It takes 3 buckets of litter to fill it. Anyway, they all share and share alike. In fact, I used to have 6 boxes but cut back because they have their favorites, for some reason, and I couldn't see any reason to have so many when they were only using certain ones the most anyway. So I just use these great big ones and scoop regularly. I just make sure I keep a consistant level of litter in the boxes and use a premium brand of litter. I NEVER have to empty and clean the boxes.