How Often You Will Empty the Drawer With Two or Three Cats

A drawer fills with clumps, not with waste. A day's urine clumps and stool take up far more room than their own volume, and clumps stack with air between them. So the useful planning figure is the space a cat's output takes in a drawer, and the best evidence for it is what makers say when they are being careful.

PetSafe's SmartSpin user guide expects its 6-litre drawer to need emptying about once a week for one cat, which is 0.86 litres a day. Its OpenSky guide expects 8.5 litres to last two weeks, 0.61 a day. CATLINK rates the 7-litre Scooper SE at seven days, 1.0 a day. 0.7 litres sits in the middle of those, and it is the figure used on every page here.

It is a planning number, not a measurement. A small cat on wet food will fill a drawer more slowly, a large cat on dry food faster. The point is to compare every box on the same assumption.

Days for one, two and three cats come from the drawer volume alone; the last column is the maker's own one-cat claim, marked where it is more than a quarter beyond the arithmetic.

The usual guidance for ordinary boxes is one per cat plus one. Automatic boxes change the reason behind it, since the litter is clean for the next cat within minutes, but not the territorial part: some cats will not share, and a single box is a single point of failure when it jams or needs a deep clean.

Makers' cat ratings are the maximum the mechanism tolerates, not a recommendation. With three or more cats the drawer becomes the limit well before the mechanism does, and a second box halves the emptying as well as giving a nervous cat an alternative.