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How Many Litter Boxes Do I Need?

The n+1 rule for litter boxes, and how to place, size and clean them so your cat actually uses them, from feline veterinary guidelines.

Choolip Team6 Oct 2026 · 7 min read

Tabby cat stepping out of a large open cat litter box, with a second box placed in a separate spot down the hallway

You need one cat litter box per cat, plus one extra. One cat means two boxes, and three cats means four. Cornell, the ASPCA and the feline veterinary guidelines all give the same rule.

Where they go matters almost as much. Two boxes side by side count as one, and a box next to a noisy washer may as well not be there. Here is how to set them up so your cat actually uses them.

Why does one cat need two boxes?

Because cats are particular about where they go. Merck's veterinary manual notes that most cats prefer separate places for urine and for feces. A second box gives them that choice.

A spare also covers the moments when one box is dirty, blocked, or in a room your cat doesn't want to enter. The AAFP and ISFM house-soiling guidelines recommend two boxes in separate locations even in a single-cat home.

In homes with more than one cat, the extra box matters more. The same guidelines say there should be enough boxes that cats never have to run into each other to use one.

It is worth knowing where the rule comes from. Those guidelines call "one more box than cats" a historical rule of thumb. It rests on expert experience and on how cats behave, more than on a trial that tested box counts head to head.

A surprising finding from a big survey

A 2023 study in the Journal of Feline Medicine and Surgery looked at 3,106 cats in Italy. About 17% of them had house-soiled, meaning they went somewhere other than the box.

Oddly, homes with two or more boxes had higher odds of house-soiling than homes with one, even after the authors accounted for how many cats lived there.

The authors' explanation is reassuring. Owners likely added boxes because a problem had already started. They write that more boxes should be seen as an attempt to fix house-soiling, never as its cause.

Where should I put the litter boxes?

Somewhere quiet, private and easy to reach at any hour. That is Cornell's description of the spot most cats prefer, and it should be well away from their food and water bowls.

Spread the boxes out. An owner guide from the AAFP and ISFM explains that your cat sees boxes close together as one large litter box.
Put one on every floor of a multistory home. Both the ASPCA and the guidelines recommend this.
Skip the laundry room if the machines are loud. The ASPCA names spots next to a washer or dryer, and busy hallways, as places to avoid.
Leave an exit. The ASPCA notes that cats like to see people or other animals coming, and they like more than one escape route.
Avoid dead ends where a cat could feel trapped, especially in a home with more than one pet.

If space is tight and two boxes must share a room, the AAFP and ISFM guidelines suggest placing them at right angles to each other, rather than in a row.

A cat that keeps going in one particular corner is telling you something. The owner guide suggests putting a box near the place your cat has been going instead.

How big should a litter box be?

Bigger than most of what's on the shelf. The 2021 AAHA/AAFP Feline Life Stage Guidelines say a box should be at least one and a half times the length of your cat, and that most commercial boxes are too small.

The sources measure that length a little differently. The AAHA/AAFP guidelines measure from nose to the tip of the tail. The AAFP/ISFM guidelines measure from nose to the base of the tail. Either way, a roomy box wins.

The research backs this up. The AAFP/ISFM guidelines describe a study in which adult cats chose a box of 34 by 15 inches (86 by 39 cm) over a smaller one.

Kittens and older cats need something different. Cornell advises boxes with low sides for both, so they can step in and out without a climb. Our guide on how to litter train a kitten covers the early weeks.

Covered or open?

The sources disagree, which is useful to know before you buy. Cornell says most cats prefer an uncovered box that lets odors escape and gives a view all around. The ASPCA agrees that most cats don't like lids.

The AAFP/ISFM guidelines are more neutral. They report cats as equally divided between large covered boxes and open ones, and they suggest open boxes partly because they are easier for you to check.

If you already use a covered box and your cat uses it happily, there is no need to change it. If you're starting fresh, an open box is the safer first choice.

What litter, and how deep?

Fine, unscented, clumping litter suits most cats. The AAHA/AAFP guidelines report that most adult cats prefer clumping litter and plain, unscented types.

For depth, Cornell and the ASPCA say most cats like about one to two inches. The AAFP/ISFM guidelines set a minimum of 1.25 inches (3 cm).

Leave out the extras. The guidelines advise against liners, slotted grills and deodorizing powders, and the ASPCA adds that most cats dislike liners. Our guide to the best cat litter compares the main types.

How often should I clean the litter box?

Scoop every day. Every source agrees on that, and the AAFP/ISFM guidelines set once a day as the minimum.

The Italian survey shows why it matters. Compared with boxes scooped twice a day, boxes scooped once a day carried 1.33 times the odds of house-soiling. Boxes scooped only three times a week carried 2.28 times the odds.

For a full clean, advice ranges from weekly to monthly. The ASPCA suggests replacing all the litter and washing the box once a week. The AAFP/ISFM owner guide says every one to four weeks.

Wash with hot water and unscented soap, or plain water. The ASPCA also lists baking soda.
Avoid strong chemicals and anything ammonia-based. The owner guide warns against both.
Top up with fresh litter after scooping, so the depth stays even.

If daily scooping is hard to keep up with, an automatic box is one option. Our look at whether a self-cleaning litter box is worth it covers the trade-offs.

What if my cat stops using the box?

Start with a vet visit. Cornell and the ASPCA both say medical problems should be ruled out before treating it as a behavior issue.

Daily scooping has a hidden benefit here. You see what your cat leaves behind, so you notice early when something changes.

Call your vet promptly if your cat:

goes in and out of the box often but passes only small amounts of urine
strains in the box with little or nothing coming out. The ASPCA warns this can be very serious and needs a vet right away.
has blood in the urine
cries or meows while trying to go
starts going outside the box when they never used to

Once your vet has ruled out a medical cause, look at the setup. Count the boxes, check where they sit, and make sure they're clean and big enough.

Questions new cat parents ask

How many litter boxes do I need for 2 cats?

Three. The rule is one per cat plus one, placed in different spots rather than lined up together.

Can two cats share one litter box?

The guidelines advise against relying on one shared box. Enough boxes in separate places means no cat has to wait or face another cat to go.

Is it okay to keep the litter box in the bathroom?

It can work if the room is quiet, the door stays open and your cat can reach it at any hour. Keep it away from food and water bowls.

How often should I change cat litter completely?

Every one to four weeks, depending on the source and how many cats use the box. The ASPCA suggests weekly. Scoop daily in between.

Where should I put a litter box in a small apartment?

Choose two quiet spots apart from each other, away from food and loud appliances. If they must share a room, set them at right angles.

Sources

This article is for general information and is not veterinary advice. Talk to your vet about your own cat — they know the animal in front of them.

Choolip products are food supplements, not medicine. They are not intended to diagnose or manage any medical condition. If your cat has been diagnosed with a condition, their diet should be set by your vet.

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