It's ideal, but not necessary if your kitty will pee and poop in the same box. Some kitties are bit persnickety and won't. I have 4 cats and they all prefer to use the same box, but we still have 3 for them. One of the boxes is seldom used, but we leave it out for them.
Well, thank you all! It's an apartment--saving up for that ranch/pipe dream house. Yes, he's really good about using it, too. Not missed the box in over 3 years. I feel a little better now. Maybe when he gets up there in years, I'll add another. Robin is a funny one--prefers his box close to his food n water. (And my bed lol). I shouldn't mess with my good luck, but I really don't like the food n water that close. But that's for another day! As long as there's no medical reason to have another box, I'll keep as is for now, I guess.
During the eighties I was a teenager, during that time I lived in a 900sq ft trailer with 3 cats and 1 litter box. The cats where great though they never had an accident. They did destroy our Christmas tree when we went out of town for a week with them in the house! They broke almost every ornament! The tree was on the floor. My Mom grew tired of them after that incident they became indoor/outdoor cats.
I wouldn't get an extra box unless necessary. Just more to clean. We have two cats and two boxes. We had one upstairs and one downstairs but they don't really use the upstairs one anymore so we've moved it down. Though I have seem them both use the same box at the same time. They really do share everything. (they are litter mates)
For a smaller place I don't think its necessary. I live in a 750 sq ft apt and it would be kinda ridiculous to have 2 litter boxes. One worked out great! Now I have 2 cats and still have that 1 litterboxes. But it is automatic scooping with crystal littler so the poo goes into its special compartment after 10 minutes.
I'll go with the old saying: If it ain't broke; don't fix it!
My 2 are litter mates. We got away with one box for years! We had a Litter Maid; so it did a lot of the work for us.
When the 2nd of those died; we went for a high sided traditional box while leaving the non-functioning Litter Maid in its spot. One of the girls almost immediately started using one to pee and the other to poo. So now we have 2 of those high sided boxes in the laundry room/closet. Its a bit of a pain because I'm leaning over the boxes to do the laundry (front loaders) and you have to be careful not to drop any clothing in the box. But if it keeps them going in the right place I can deal with that!
I do wonder if we could still get away with one if we were still in a smaller place; but I dont think we could go back to just 1.
I think with one cat, one litter box should do but sometimes, trial and error kicks in. I believe the rule of thumb is one box per cat although I have heard where there is more than one cat, to have one extra litter box. Every circumstance is different. I have two cats but four litter boxes. I did this for a reason. When I lost my Sam, I adopted another cat to keep my Maggie company. Well, Maggie was not so happy about that so she would do her business right at the entrance of the two litter boxes which of course the new cat, Pepper did not really liked. Pepper in turn, did the same thing to her so I figured before the possessiveness got out of hand, I purchased a third litter box. Now, as to the fourth box, well, I saw a corner style box that I really liked and did not want to get rid of one of the others, hence, they have four. Of course, when my Maggie passed away, I adopted another little girl and she takes great delight in using all four of them. They do require more cleaning but I am very particular about it and they get cleaned out three times a day, if needed. Pepper only uses two. He likes to pee in one and have bowel movements in the other. You just have to see what works for your kitties.
I have a ranch with 2 cats and 3 boxes. Yours, mine, and ours. My cats DO NOT get along. I notice when he makes a deposit in her box, she goes to the little used third box, until I get to scooping his stuff out. It is a territory battle with these two. The system works, we have never had an accident outside the box!
We have two for three because we simply don't have room for another in a reasonable place. One is very clearly the pee box, the other is the poop box. I am amazed at how they work stuff like that out.
My two adult cats share a large litter box. They're siblings and have never had a problem with it. I do keep it very clean, and put out an extra box when we go away and the pet-sitter will only be scooping once a day. So yes, I think one box for one cat is fine!