Tray logistics are arithmetic before they are preference. The working rule is one tray per cat plus one extra, each big enough for the cat to turn around in — roughly one and a half times body length — filled to about 3-5 cm with a fine, unscented, clumping litter, and placed in separate spots rather than lined up in a row. Two trays side by side behave like one tray in a house where a cat is guarding or lurking.

Scooping is the maintenance job that decides whether the tray stays acceptable: at least once a day, with a full litter change and a wash when the tray starts to hold odour. Liners, deodorising powders and hoods all reduce usability for many cats, and a covered tray concentrates smell exactly where the cat has to stand.

When a cat stops using the tray, that is information. International Cat Care is direct about it: soiling indoors is a sign that something is wrong — illness or stress — and punishment makes it worse, because it adds fear to a problem that already has a cause. It is worth checking the medical side with a veterinary team rather than experimenting with deterrents. Practical next steps: litter box setup 101, the cleaning routine, and the litter box planner for multi-cat maths.

Sources: International Cat Care — Choosing a litter tray for your cat, International Cat Care — Soiling indoors.