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Short answer: one litter box per cat, plus one, in different rooms, and at least one on every floor. Each box should be at least 1.5 times your cat’s length, uncovered, with a few inches of unscented litter, scooped daily and washed weekly. Keep boxes away from food bowls and the washer and dryer.
The n+1 rule
Shelter and veterinary guidance agrees on a simple formula: the number of cats plus one. Two cats, three boxes. Three cats, four boxes. The San Francisco SPCA adds a detail most people miss: the boxes have to be in different rooms to count separately. Two boxes side by side in the laundry room look like one large box to a cat.
Why so many? Cats like a clean box, some prefer one box for urine and another for stool, and in multi-cat homes one cat can guard a box or a hallway. Extra boxes in different places mean every cat always has an option.
How many boxes, and how big, for your home
Litter box calculator
Measure your largest cat from nose to base of tail (in inches).
How big should a litter box be?
The San Francisco SPCA’s guidance is that a box should be at least 1.5 times the length and width of your cat. For an adult cat about 18 inches long, that is a box roughly 27 inches long, larger than most boxes sold as “large”.
- Go bigger, not taller. A large, open box lets a cat turn around and dig without stepping in old waste.
- The storage bin trick: a large clear plastic under-bed or storage bin, with the lid off, makes an inexpensive oversized box. Cut a low entry in one side for kittens, older cats or cats with stiff joints.
- Seniors need a low entry. If your cat hesitates to step in, a box with one low side often fixes it.
Litter box setup we would buy
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30 × 20 inches, open top, scatter shield.
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How we chose
- We started from the sizing and safety guidance in this article and checked each product’s listed dimensions against it.
- We favored long-running, widely bought products with a large volume of owner feedback, and read the complaints as closely as the praise.
- We checked each listing on October 16, 2026 for stock and U.S. delivery.
- We have not tested these products with our own pets. Picks are based on specifications, instructions and owner feedback.
Best big box: IRIS USA XX-Large High-Sided Litter Box
An open-top plastic box with high sides and a scatter shield. At 30 inches long it meets the 1.5-times rule for cats up to about 20 inches from nose to base of tail.
- Big enough to turn around and dig.
- Uncovered, which most cats prefer.
- High sides keep litter in.
- Downside: Takes floor space; measure the spot first. Older cats with stiff joints may find the sides high.
Skip it if your cat is a senior with arthritis; choose a box with one low side instead.
Check it on AmazonBest litter: Dr. Elsey’s Ultra Unscented Clumping Clay Litter
An unscented, clumping clay litter that fits the shelter guidance to avoid scented litter. One of the best-selling cat litters on Amazon for years.
- Unscented, as SF SPCA guidance recommends.
- Hard clumps are easy to scoop daily.
- Downside: Clay is heavy to carry and store.
Skip it if your cat already uses a different litter happily; switch slowly if at all.
Check it on AmazonBest mat: Pieviev Double-Layer Litter Mat
A honeycomb mat that catches litter from paws; lift it and the litter falls through the top layer for easy emptying.
- Keeps litter from tracking through a small apartment.
- Waterproof base protects floors.
- Downside: Smaller than the XX-Large box; use two mats or a larger size in front of big boxes.
Skip it if your box sits on a hard floor you can sweep easily.
Check it on AmazonAlso useful
- A sturdy scoop: a deep aluminum litter scoop for daily scooping.
Where to put the litter boxes
- Quiet, but not hidden away. A corner a cat can reach easily, where it can see someone coming.
- Away from food and water. Cats do not like to eat next to their toilet.
- Away from the washer and dryer. A sudden spin cycle can put a cat off a box for good.
- One on each floor in a multi-story home.
- Not in a dead end in multi-cat homes, so no cat can be trapped by another.
In a small apartment, the bathroom, a bedroom corner and a hallway nook can each take a box. A box hidden inside furniture can work if the opening is large and your cat uses it, but follow the same rule: if it is covered, watch whether your cat is happy with it.
Litter, liners and cleaning
| Do | Avoid |
|---|---|
| Several inches of litter so your cat can dig | A thin layer that leaves the floor of the box exposed |
| Unscented litter | Scented litter, air fresheners right next to the box |
| Scoop every box at least once a day | Letting waste build up for several days |
| Empty and wash weekly with mild dish soap | Harsh detergents and strong-smelling cleaners |
| Uncovered boxes | Box liners, which many cats dislike |
If you change litter type, do it gradually: mix the new litter into the old over a week or two, or offer the new litter in one extra box and see which your cat chooses.
Litter box setup checklist
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When it is not the litter box
If a cat suddenly stops using the box, see your veterinarian before changing the setup. Peeing outside the box can be a sign of a medical problem such as a urinary tract issue. A cat, especially a male cat, that strains in the box and passes little or no urine needs a veterinarian the same day: a urinary blockage is an emergency.
Frequently asked questions
How many litter boxes should I have for 2 cats?
Three. The usual rule is one litter box per cat plus one extra, and the boxes should be in different rooms. Two boxes side by side are treated by cats as one big box.
Is one litter box enough for one cat?
The n+1 rule suggests two boxes for one cat, in different locations. Many single cats do manage with one, but a second box helps if the cat is old, if your home has more than one floor, or if the cat has ever gone outside the box.
How big should a litter box be?
At least 1.5 times the length of your cat, measured from nose to base of tail, according to guidance from the San Francisco SPCA. For a typical adult cat that is larger than most standard boxes, which is why many owners use a large plastic storage bin instead.
Do cats prefer covered or uncovered litter boxes?
Most cats dislike covered boxes, especially in homes with several cats, according to the San Francisco SPCA. Covers trap odor inside where the cat smells it, and they can leave a cat feeling cornered.
How often should I clean the litter box?
Scoop each box at least once a day, and empty and wash it with mild dish soap once a week. Avoid harsh detergents, liners and scented litters, which many cats dislike.
Where should I put the litter box?
Somewhere quiet and easy to reach, away from food and water bowls and away from noisy appliances such as the washer and dryer. In a home with more than one floor, put a box on each level.
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