Cat Litter Calculator

One box per cat, plus one

This is the standard veterinary behaviour recommendation and it is the single most effective change most multi-cat households can make. Three cats means four boxes.

The boxes must be in separate locations. A row of four boxes along one wall is one location to a cat, and it does nothing to solve the resource competition the rule exists to address. Spread them across rooms and floors.

One cat still wants two boxes. Cats frequently prefer to urinate and defecate in different places, and a second box removes the most common reason a single cat starts going elsewhere.

Depth and box size

Seven to ten centimetres of clumping litter is the usual guidance and most people use far less. Shallow litter lets urine reach the base of the box, so clumps stick and break up when you scoop, which leaves wet fragments behind — and those fragments are the smell.

Deeper litter also tracks less, because the cat digs within the layer rather than scraping the bottom and flinging granules over the side.

Box size matters as much as count. The box should be roughly one and a half times the cat's body length, nose to tail base, and most commercially sold boxes are smaller than that. A large storage tub is a cheap, effective litter box and many cats prefer one.

Placement, and the mistakes that cause accidents

Away from food and water. Cats will not toilet where they eat, and a box beside the feeding station is a box that gets avoided.

Away from noisy appliances. A washing machine that starts a spin cycle while a cat is in the box can put it off that spot permanently.

Accessible. An arthritic older cat may simply be unable to climb into a high-sided box or get down a flight of stairs to reach it, and that is a very common and very missable cause of accidents in an old cat. Cut a low entry into one side, or buy a shallow box, and put one on every floor the cat uses.

Uncovered, unless you know your cat prefers a hood. Hoods trap odour inside the box, which suits you and not the cat.

When it is medical, not behavioural

Changes in litter box behaviour are a medical sign first. Straining, frequent small visits, blood, crying in the box or toileting outside the box in a previously reliable cat all warrant a vet.

A male cat straining in the box and producing little or nothing is a suspected urinary blockage. That is life-threatening and needs a vet immediately, including out of hours. Blocked cats can die within a day or two.

Once medicine is ruled out, clean any marked spot with an enzymatic cleaner rather than an ammonia-based one. Ammonia smells like urine to a cat and invites repeat marking.

Common questions

How many litter boxes do I need?

One per cat plus one, in separate locations. Three cats means four boxes, spread across rooms rather than lined up along a wall — a row is one location to a cat. Even a single cat does better with two, because many cats prefer to urinate and defecate in different places.

How deep should cat litter be?

Seven to ten centimetres of clumping litter. Most people use much less, and shallow litter lets urine reach the base so clumps stick and break up when scooped, leaving wet fragments that smell. Deeper litter also tracks less.

What size should a litter box be?

Roughly one and a half times the cat's body length from nose to tail base. Most boxes sold in shops are smaller than that. A large plastic storage tub makes an excellent, cheap litter box and many cats clearly prefer one.

Where should I put the litter box?

Away from food and water, away from noisy appliances, and somewhere the cat can always reach it — including a box on every floor for an older cat. Arthritis makes climbing into a high-sided box painful, which is a very common cause of accidents in old cats.

My cat has started going outside the box. What now?

See a vet first. Straining, frequent small visits, blood or crying in the box are medical signs, and a male cat straining and passing nothing is a life-threatening emergency. After that, check the basics and clean marked spots with an enzymatic cleaner — never an ammonia-based one, which smells like urine to a cat.