Tell us how many cats share your home and how long the biggest one is. You get the box count, the minimum box size that still works, and where each box has to go. It takes twenty seconds, and it is the setup mistake behind most litter box problems.
How many litter boxes do you need?
One box per cat, plus one. The extra box is not a spare. In a multi-cat home, boxes are territory, and a cat that has to wait for the only box will eventually stop using it. This is the rule the calculator applies.
| Cats in the home | Boxes you need | On each floor |
|---|---|---|
| 1 cat | 2 boxes | At least 1 |
| 2 cats | 3 boxes | At least 2 |
| 3 cats | 4 boxes | At least 2 |
| 4 cats | 5 boxes | At least 3 |
| 5 cats | 6 boxes | At least 3 |
Spread the boxes out rather than lining them up. Keep them at least 60 cm apart — boxes placed side by side are treated as a single spot by the cats using them. Never put a box where the cat can be cornered.
How big should a litter box be?
The box should be about 1.5 times the length of the cat, measured nose to the base of the tail. Most boxes sold as “standard” are around 50 cm long, which is too small for a full-grown cat.
| Cat length (nose to tail base) | Minimum box length | Minimum box width | Who this fits |
|---|---|---|---|
| 40 cm | ≥ 60 cm | ≥ 40 cm | Small or young cat |
| 45 cm | ≥ 68 cm | ≥ 40 cm | Average adult cat |
| 50 cm | ≥ 75 cm | ≥ 40 cm | Average adult cat |
| 55 cm | ≥ 83 cm | ≥ 40 cm | Large breed, or a long cat |
| 60 cm | ≥ 90 cm | ≥ 40 cm | Large breed, or a long cat |
Width matters as much as length. A cat has to be able to turn around without its body touching both sides, which is where most commercial boxes fail first.
Placement and cleaning rules
| Rule | What it means |
|---|---|
| Scoop at least 2× a day | Cleanliness decides whether a cat uses a box far more than style or litter type does. |
| Full change every 7 days | More often in a multi-cat home, and more often in warm weather. |
| Never beside food or water | Cats will not eat next to where they toilet. It also puts them off drinking. |
| Avoid noisy, closed-off spots | Laundry rooms, boiler cupboards and dead ends turn a box into a trap if another cat blocks the exit. |
| Entry under 10 cm for a stiff cat | Or cut a low entry into a high-sided box. A cat that has to step up will go elsewhere instead. |
Based on the AAFP and ISFM feline environment needs guidelines. Open and covered boxes test about the same for cat preference — what drives the choice is how clean the box is. Vets still favour open boxes, because a large cat cannot posture properly in a small covered one and covered boxes hold odour in.
Why the rule is “one per cat, plus one”
It is not about capacity. In a home with more than one cat, a litter box is territory. If there are fewer boxes than cats plus one, the least confident cat in the house has to cross another cat’s space every time it needs to go — and the predictable result is a cat that holds on, or goes somewhere else entirely.
The extra box also gives you something practical: when a box is being washed, nobody is left without one. That matters more than most owners expect, because a single missed day is enough to start a habit that is very hard to undo.
Size is where almost every commercial box fails
A box should be about one and a half times the length of the cat, measured from the nose to the base of the tail. Many boxes sold as standard are around 50 cm long. That is shorter than the rule allows for a full-grown cat, and it is the reason a cat will hang its back end over the edge no matter how clean the litter is.
Width matters just as much. A cat has to be able to turn around without its body touching both sides. If it cannot, it will use the box less, or not at all.
What this page will not tell you
Environment is only half of a litter box problem. If your cat is going outside the box, the other half is medical, and no amount of rearranging furniture will find a bladder infection, crystals, kidney disease or arthritis. A male cat straining in the box and passing little or nothing is an emergency that can become fatal within a day — that is a vet visit right now, not a change of litter.
We also do not recommend specific boxes. The result you get is a specification to shop against, including the internal litter guidelines the rules come from.