Does the n plus one rule apply in a small home too?

Yes, and it matters even more, because in a small space a box is more likely to end up in a walkway or next to a source of noise. In a studio flat the two boxes can go at opposite ends of the room, as long as they are not side by side and each has a clear exit route.

Are hooded boxes acceptable?

It depends on the cat. A hood reduces litter scatter and contains odour for people outside, but concentrates it for the cat inside and removes an escape route. If you have a hooded box and an elimination problem, take the hood off for two weeks and see whether anything changes.

Can I use scented litter to keep the smell down?

Better not. Fragrance masks odour for us but is far more intense for the cat, and in preference tests unscented litters are chosen more often. Odour is controlled with daily cleaning and the correct number of boxes, not with fragrances.

My cat urinates in the box but passes faeces on the floor: why?

That is a frequent pattern and often has a physical or environmental cause: pain during defecation, a box too small to turn around in, disliked litter or an overly exposed location. Add a larger box in a quiet spot and, if the behaviour persists beyond two weeks, have the cat assessed by a vet.

Safe home and enrichment45 minLevel: BeginnerUpdated on August 4, 2026

How many litter boxes you need and where to put them

Number, size and placement of litter boxes at home: the n plus one rule, correct dimensions, the cleaning routine and the signs of refusal.

Audience: Pet owners
Species: Cat
Scope: Valid everywhere

What you need before you start

Un metro a nastro per misurare il gatto dal naso alla base della coda e le cassette che già possiedi
Una pianta mentale o disegnata della casa, con i piani e le stanze in cui il gatto si muove abitualmente
Substrato sufficiente per riempire ogni cassetta con uno strato da 3 a 5 cm
Una paletta per cassetta e un contenitore chiuso per lo smaltimento quotidiano

When a cat stops using the litter box, the first thing to review is not temperament but arithmetic: how many boxes there are, how big they are, where they sit and how often they are cleaned. These are four variables the owner controls completely, and in most homes none of them was ever set deliberately: the box ended up in the bathroom because there was space, and it stayed there for years. This guide explains how many boxes are genuinely needed, how to size them for the cat you actually have, where to place them and how to change litter without triggering refusal. It takes about forty five minutes of practical work.

How many boxes are genuinely needed

The working rule is simple: one box per cat, plus one. With one cat you need two boxes, with two cats you need three. This is not excessive: a single box means that when it is dirty, occupied or blocked by another animal, there is no alternative and the cat picks another spot in the house.

Number of cats, recommended boxes and distribution
Cats at home	Boxes	Recommended distribution
One	Two	In two different rooms, ideally on different floors
Two	Three	Never all in the same room, never in a row
Three	Four	At least one per area of the house in regular use
Four	Five	Distributed according to each cat's resting areas too
House on two floors	At least one per floor	An old cat will not manage the stairs in time

Where to put them and where never to

The ideal spot is quiet but not isolated, with at least two exit routes and no sudden noises nearby. A cat that feels trapped while in the box stops using it, and that refusal tends to consolidate quickly.

Good placements and placements to avoid
Placement	Verdict	Reason
Quiet corner with two exit routes	Excellent	The cat can watch the room and never feels cornered
Low traffic room that stays reachable	Good	Privacy without isolation
Next to the food bowl	Avoid	Strong conflict between elimination and eating areas
Next to a washing machine or boiler	Avoid	A sudden noise creates a lasting negative association
Cupboard with a single door	Avoid	No escape route if another animal appears
Balcony or a room kept locked	Avoid	Access can be missing exactly when it is needed

Which box and which litter to choose

Size is calculated from the cat, not from the packaging. The box should be at least one and a half times the length of the cat measured from nose to base of tail, so it can turn, dig and cover without touching the sides. Boxes sold as standard are often too short for an average adult cat.

Box features and how to choose them
Feature	Criterion	Note
Length	At least 1.5 times the cat from nose to tail base	Better too large than too tight
Side height	Low on one side for kittens and old cats	Arthritis makes climbing a high side painful
Hood	Optional, many cats prefer an open box	A hood traps odour and removes exit routes
Litter depth	3 to 5 cm	Less prevents digging, much more gets scattered out
Litter type	Fine grained, clumping, unscented	Strong fragrances reduce acceptance
Plastic liners	Better avoided	Claws puncture them and the feel underfoot changes

Setting up and changing without causing refusal

Measure the cat and the boxes you own
Measure from nose to base of tail with the cat relaxed and compare that with the internal length of your boxes. Any box that comes up short should be replaced before anything else is attempted.
Sketch the floor plan and mark where the cat lives
Mark resting spots, transit routes and rooms the cat almost never enters. Boxes belong in the areas actually used, not in the ones that happen to be free for us.
Place the new boxes in different rooms
Add the missing boxes according to the n plus one rule, spreading them across different rooms and floors. Keep the old ones in service too: nothing is removed at this stage.
Fill with a layer of 3 to 5 cm
Measure once with a ruler to learn what that looks like in your container, then repeat by eye. Too thin a layer prevents digging, too thick a layer ends up on the floor.
If you change litter, offer a choice
Put a box with the new litter next to one with the old and watch which gets used over a week. This preference test is more reliable than any general recommendation.
Move to the new litter gradually
Once the choice is confirmed, replace about a quarter of the old litter every three days. An abrupt switch is one of the most frequent causes of elimination outside the box.
Observe for two weeks before removing anything
Note which box gets used and for what: many cats use one box for urine and another for faeces. Only after two weeks can you decide whether a station is genuinely redundant.
Clean accidents with an enzymatic product
Ammonia based cleaners smell like urine and invite repetition in the same spot. Use an enzymatic product, applied over the whole affected area and left to work for the stated time.

The cleaning routine that keeps it all stable

Cleaning is the variable that weighs most on daily acceptance. A dirty box is the most frequent reason a cat that always used the litter starts looking for alternatives, and the tolerance threshold varies widely between individuals.

Task, frequency and practical note
Task	Frequency	Note
Removing faeces and clumps	At least once or twice a day	Better after each use for a fussy cat
Topping up the litter	When the layer drops below 3 cm	Always keep the same depth
Full emptying and washing	Every two to four weeks with clumping litter	Weekly with non clumping litter
Washing the box	Hot water and a neutral detergent	No bleach and no scented products
Replacing the box	When the plastic is scratched and dull	Scratches hold odour permanently
Checking amount and appearance	At every clean	Changes in volume or consistency should be noted

Signs that need a vet, not another box

The environment explains many cases of elimination outside the box, but not all of them. Some signs point to a medical problem and must be assessed before any environmental change, because waiting worsens the outcome.

The cat goes in and out of the box repeatedly producing little or no urine: this is an emergency, especially in males.
It vocalises or holds a tense posture while urinating or defecating.
Blood appears in urine or faeces, even in small amounts.
Urine volume rises noticeably, with clumps much larger than usual.
The cat drinks far more than usual and the box fills up faster.
Elimination outside the box appears in a cat that never did it before.
The cat licks the genital area or the belly persistently.

Frequently asked questions

Does the n plus one rule apply in a small home too?: Yes, and it matters even more, because in a small space a box is more likely to end up in a walkway or next to a source of noise. In a studio flat the two boxes can go at opposite ends of the room, as long as they are not side by side and each has a clear exit route.
Are hooded boxes acceptable?: It depends on the cat. A hood reduces litter scatter and contains odour for people outside, but concentrates it for the cat inside and removes an escape route. If you have a hooded box and an elimination problem, take the hood off for two weeks and see whether anything changes.
Can I use scented litter to keep the smell down?: Better not. Fragrance masks odour for us but is far more intense for the cat, and in preference tests unscented litters are chosen more often. Odour is controlled with daily cleaning and the correct number of boxes, not with fragrances.
My cat urinates in the box but passes faeces on the floor: why?: That is a frequent pattern and often has a physical or environmental cause: pain during defecation, a box too small to turn around in, disliked litter or an overly exposed location. Add a larger box in a quiet spot and, if the behaviour persists beyond two weeks, have the cat assessed by a vet.

What to do next

Count the boxes and apply the n plus one rule, measure the cat from nose to tail base to confirm every box is at least one and a half times that length, then spread them across different rooms and floors away from food and noise. Scoop at least once a day and change litter only gradually: if straining without urine output appears, go to the clinic immediately.