How Many Litter Boxes per Cat? Litter Box Calculator

By Marcos Ortega · Updated October 25, 2026 · Runs in your browser; nothing you type is sent anywhere.

Cornell’s Feline Health Center lists an aversion to the litter box, along with medical problems, among the reasons cats go outside it. Feline veterinary groups give simple rules for how many boxes to have and how big they should be; the calculator applies them to your home.

The rules

Question	Guidance	Source
How many boxes?	One per cat, plus one extra, in different places	AAFP/ISFM; Cornell
Several floors?	A box on each level of the home	AAFP/ISFM
How big?	1.5 × the cat’s length, nose to base of tail	AAFP/ISFM
Where?	Apart from each other, and well away from food, water and resting places	AAFP/ISFM
Litter?	Most cats prefer soft, unscented clumping litter, about 1–2 inches deep	AAFP/ISFM; Cornell
Cleaning?	Scoop at least once a day; wash the box every 1–4 weeks with soap and hot water	AAFP/ISFM

The calculator takes the larger of “cats + 1” and “one per floor”.

Boxes = the larger of (number of cats + 1) and (number of floors)
Minimum box length = 1.5 × cat's length (nose to base of tail)

Worked examples

Example 1: two cats in a one-floor apartment, the larger cat 18 in long. Boxes: 2 + 1 = 3. Minimum box length: 1.5 × 18 = 27 in.

Example 2: one cat in a three-floor house. 1 + 1 = 2, but one per floor gives 3 boxes.

Example 3: a cat 45 cm long. 1.5 × 45 = 67.5 cm.

Why it matters

The AAFP/ISFM environmental needs guidelines say each cat should have a choice of key resources, such as a minimum of two toileting areas, set well apart from food and resting places. Cornell notes that one box per cat plus one decreases competition between cats.

Limitations

Rules of thumb, not a guarantee. Some cats are happy with less; others need more or different boxes and litter.
Sudden changes are a vet question. Medical problems can cause house soiling. Cornell advises taking a cat that soils the house to the vet for an examination and tests.

Frequently asked questions

How many litter boxes do I need for 2 cats?

Three: one per cat plus one extra, the rule of thumb given by the American Association of Feline Practitioners (AAFP) with the International Society of Feline Medicine (ISFM), and by Cornell's Feline Health Center.

Is one litter box enough for one cat?

The same rule gives two boxes for one cat. The AAFP/ISFM environmental needs guidelines also say a cat should have a choice of each key resource, giving two toileting areas as an example of the minimum.

How big should a litter box be?

AAFP/ISFM: 1.5 times the length of the cat from the nose to the base of the tail. Cornell adds that larger cats need bigger boxes, and kittens and elderly cats need boxes with low sides.

Can I put the litter boxes next to each other?

Better not. AAFP/ISFM advise keeping boxes apart in different locations, because a cat may see boxes next to each other as one large box.

How often should I clean the litter box?

AAFP/ISFM say to remove waste at least once a day, add litter as needed, and wash the box every 1–4 weeks with soap and hot water only.

Sources

American Association of Feline Practitioners (AAFP) and International Society of Feline Medicine (ISFM). Why is my cat urinating and/or defecating outside of the litter box? (client brochure, 2014 House-Soiling Guidelines) (2014). Checked October 25, 2026.

Cornell Feline Health Center. Feline Behavior Problems: House Soiling. Checked October 25, 2026.

Ellis SLH, Rodan I, Carney HC, et al. Journal of Feline Medicine and Surgery 15:219–230. AAFP and ISFM Feline Environmental Needs Guidelines (2013). Checked October 25, 2026.