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Danny's Cats

Litter and hygiene

N+1 litter box rule

Also called One box per cat plus one

Updated

What is the N+1 litter box rule?

The N+1 litter box rule says a home should have one litter box per cat plus one extra, so two cats get three boxes. Cornell, the ASPCA and Battersea all give the formula. The AAFP and ISFM house-soiling guidelines call it a historical rule of thumb rather than an absolute requirement, and say a single cat should have two boxes.

Where should the extra boxes go?

Extra litter boxes belong in different places, not side by side. The AAFP and ISFM guidelines say cats perceive boxes placed next to each other as one large box, and recommend at least one box on each level of a multi-level home. Cornell also advises placing multiple boxes in different areas of the house.

Is the N+1 rule based on evidence?

The N+1 rule is not firmly based on evidence. The AAFP and ISFM guidelines call it a historical rule of thumb and not an absolute requirement. Their guiding principle is enough boxes in enough places that each social group of cats has its own toileting sites. Cats that get along may share more willingly, and cats that do not should have separate litter stations.

Counting boxes that sit in one spot

Three boxes in a row count as one big box to a cat, according to the AAFP and ISFM guidelines. Spread them out so each cat can reach a box without having to pass another cat.

Questions about the N+1 litter box rule

How many litter boxes do two cats need?

Two cats need three litter boxes by the N+1 rule that Cornell, the ASPCA and Battersea give. Put them in separate places rather than in a row, so one cat cannot guard them all. Our article on where to put a litter box covers placement and compares what six authorities recommend.

Does one cat need two litter boxes?

One cat needs two litter boxes, according to the AAFP and ISFM house-soiling guidelines, which say a home with a single cat should have two boxes in two separate locations. That is also what the formula of one per cat plus one gives, so the two sources agree on a single-cat home.

Where this comes up

Sources