Most litter box problems are resource problems, not behaviour problems. Number, placement and separation all matter — and a cat that has to walk past another cat to reach the only box will eventually stop using it. Enter a household to see what the guidance works out to.
A number on its own does not solve a soiling problem. A cat that has suddenly started going outside the box needs a veterinary visit first — urinary obstruction is an emergency in male cats, and cystitis, kidney disease and arthritis all present this way before they look like anything else.
Placement matters as much as number
- Boxes in separate locations, not lined up side by side — two boxes in one room function as one resource.
- Away from food and water. Cats do not toilet where they eat.
- Somewhere with more than one exit, so a cat cannot be cornered in it.
- Reachable without stairs for older or arthritic cats — at least one box per floor.
- Large enough to turn around in comfortably; many commercial boxes are too small.
How this tool was built: methodology and sources
Two different sources say two slightly different things, and this tool reports both rather than blending them into one invented number.
The peer-reviewed guideline does not give a formula. It specifies that every cat needs a choice of each key resource — a minimum of two toileting areas — and that resources must be in separate locations, physically apart from food and water. The principle is choice and separation, not arithmetic.
The “n+1” rule — one box per cat plus one spare — comes from the Ohio State University Indoor Pet Initiative, which presents it as a practical golden rule. It is a widely used convention rather than a finding from a controlled trial, and this tool labels it as such.
The figure shown above is n+1, with a floor-by-floor minimum applied on top, because that is the more demanding of the two and satisfies both.
- Ellis SLH, Rodan I, Carney HC, Heath S, Rochlitz I, Shearburn LD, Sundahl E, Westropp JL. AAFP and ISFM Feline Environmental Needs Guidelines. Journal of Feline Medicine and Surgery 2013;15(3):219–230. PMID 23422366
- Litter Boxes. Indoor Pet Initiative, The Ohio State University College of Veterinary Medicine — source of the one-per-cat-plus-one rule. Reference page