My roommate and I live in a 3 bedroom house and we have three cats, for us that is the limit in the house. I think we'd both go nuts if we had anymore. But I think the amount you can have is a personal thing. My cats are always all over the place, they are still pretty young and my roommates cat just kind of sits on the window sill and sleeps. So I think if my two cats acted like my roommates then getting another cat in the house would be fine. So I guess it's more of a personal sanity thing. Because I would go insane if I had another Corkscrew or Tibby in the house.