How many litter boxes do you need? (The 'n+1' rule explained)
Cornell, OSU and AAHA all give the same rule of thumb: one box per cat, plus one. Cornell's example: two cats means three boxes.
The nuance from the AAFP/ISFM guidelines
- A single-cat household "should have two litter boxes in two separate locations."
- In multi-cat homes the n+1 rule "is not an absolute requirement." Socially bonded cats may share, but cats that aren't bonded "should have separate litter stations."
- "At least one litter box should be placed at each level of a multilevel home."
- "Cats perceive litter boxes located adjacent to each other as one large box." Spread them out.
- Keep food and water away from the box.
What about self-cleaning boxes?
Whisker says one Litter-Robot 4 "is suitable for up to four cats–removing the need for multiple boxes." That is the manufacturer's claim, and it differs from the vet-association rule above. If you have several cats, consider keeping at least one extra regular box. See is a self-cleaning box worth it?
Sources (opened October 21, 2026)
- Cornell Feline Health Center — Choosing and Caring for Your New Cat
- Indoor Pet Initiative, Ohio State University CVM — Litter Boxes
- AAHA/AAFP Feline Life Stage Guidelines — General Litter Box Considerations
- AAFP and ISFM Guidelines for Diagnosing and Solving House-Soiling Behavior in Cats (PMC)
- Whisker — Litter-Robot 4 (manufacturer page)