How do I choose and set up a litter tray, and stop it smelling?

Choosing the tray and litter that a cat will actually use, the depth and cleaning routine, and why scented litter makes smell worse rather than better.

Difficulty: beginner
Time: 30 min
Read: 5 min
Safety: caution

Short answer

Get a tray at least one and a half times the length of the cat, open rather than hooded, filled with three to five centimetres of unscented clumping litter. Scoop twice a day and wash the tray out fully every week or two with hot water and unscented detergent. Frequency of scooping is what controls smell, not scented litter.

How many trays you need and where they go is a separate question from what to put in them — and it is the second question that determines whether a cat uses the tray happily and whether the room smells. Cats have strong substrate preferences learned young, and most of the products marketed at owners for odour are designed around what a human finds pleasant rather than what a cat will tolerate.

Safety

Never clean a litter tray with a disinfectant containing phenols — the pine or antiseptic-smelling ones — because they are toxic to cats. Hot water and an unscented washing-up liquid or a cat-safe disinfectant is what to use. Do not flush cat litter or faeces down the toilet: it blocks drains and can carry a parasite of public health concern. Pregnant women and anyone immunosuppressed should avoid handling used litter, or wear gloves and wash their hands afterwards. A cat straining in the tray without producing urine is an emergency, particularly a male cat, and needs a vet immediately.

What you'll need

An open litter tray, large
Unscented clumping litter
A scoop and lidded bags
A litter mat (optional)
Cat-safe disinfectant (optional)

How many litter trays, and where to put them

Step by step

Buy a tray far larger than looks necessary.At least one and a half times the length of the cat from nose to base of tail, so it can turn round, dig and cover without touching the sides. Most trays sold are too small for an adult cat. A plain under-bed storage box is a cheap and excellent litter tray for a big cat.
Start with an open tray rather than a hood.Most cats prefer an open tray: they can see out, they cannot be ambushed, and it does not concentrate the smell around their head. Hoods suit the owner more than the cat. If you use one, take the flap off — cats dislike pushing through them.
Use unscented clumping litter as the default.Clumping mineral litter allows accurate daily removal of both urine and faeces, which is the whole basis of odour control. It is also the texture surveys of cat preference tend to favour. Wood pellet and paper litters are lighter and more sustainable but do not clump in the same way; silica crystals control odour well but some cats dislike the texture underfoot.
Avoid scented litter and deodorising powders.A cat's sense of smell is vastly better than yours, and a heavily perfumed tray is a common reason a cat starts going elsewhere. The perfume also masks rather than removes, so the underlying problem gets worse while you notice it less.
Fill it three to five centimetres deep, and keep it topped up.Deep enough to dig and cover properly. Too shallow and the cat cannot bury anything and the urine reaches the plastic, which is where lasting smell comes from. Too deep wastes litter and some cats dislike it.
Skip liners for most cats.Claws catch and tear them while digging, litter gets underneath, and many cats object. They rarely save the work they promise.
Scoop twice a day, every day.This is the single thing that controls smell. Remove clumps and faeces morning and evening into a bag, tie it, and put it in the general waste bin. Scooping frequency also protects the tray from being rejected — cats are fastidious and a tray with yesterday's waste in it is a tray they will start avoiding.
Do a full change and wash every one to two weeks.Empty it completely, wash with hot water and unscented washing-up liquid or a disinfectant that is explicitly safe for cats, rinse thoroughly, dry, and refill. Never use phenolic disinfectants — the ones that go milky in water and smell of pine — because they are toxic to cats.
Replace the tray itself every year or so.Plastic scratches with use, and the scratches hold urine that no amount of washing removes. A tray that smells immediately after being cleaned has reached the end of its life.
Introduce any change to litter type gradually.Cats form strong substrate preferences. To change type, mix the new litter into the old over a week or two, or better, offer a second tray with the new litter alongside the old one and let the cat choose.

Tips

A litter mat outside the tray catches most of the tracked litter and takes ten seconds to shake out. It saves more cleaning than anything else you can buy.
Store the scoop, bags and spare litter beside the tray. Scooping twice a day happens far more reliably when the equipment is where the tray is.
For a kitten, an elderly cat or an arthritic one, use a tray with a low entry point or cut a section out of one side. Stepping over a high lip is exactly what an arthritic cat stops being able to do.

Common mistakes

Using scented litter to control smell — Cats have a far better sense of smell than people, and strong perfume is a common reason they start toileting elsewhere. Scooping frequency is what controls odour.
Buying a tray sized for a kitten — A cat needs to turn round, dig and cover. A tray that is too small is one of the commonest reasons a cat goes just beside it rather than in it.
Cleaning with a pine or antiseptic disinfectant — Phenolic disinfectants are toxic to cats. Hot water and unscented detergent, or a product explicitly labelled cat-safe, is what to use.
Flushing litter or waste down the toilet — It blocks drains, and cat faeces can carry a parasite that water treatment does not reliably remove. Bag it and put it in the general waste.

If it doesn't work

Tray smells even after cleaning

Cause: Scratched plastic holding urine, or too-infrequent full changes — Fix: Replace the tray, and move to a full empty-and-wash every week. Scoop twice daily in between.

Cat goes just beside the tray

Cause: Tray too small, too dirty, or the cat cannot get in comfortably — Fix: Try a much larger tray with lower sides and scoop more often. If it persists, see the vet — this pattern often accompanies pain.

Litter is tracked all through the house

Cause: Fine litter and no mat — Fix: Use a litter mat, a tray with higher sides at the back, or a coarser litter such as wood pellets.

Cat stopped using the tray after you changed brand

Cause: Substrate preference — Fix: Go straight back to the old litter and change gradually next time, or offer both side by side and let the cat pick.

Questions people ask

What is the best cat litter?

Unscented clumping mineral litter suits most cats and gives the best odour control, because it lets you remove waste accurately every day. The best litter for your cat, though, is the one it will reliably use, so preference beats specification.

How often should a litter tray be cleaned?

Scooped twice a day, and emptied, washed and refilled every one to two weeks. Scooping frequency is what controls smell — no litter compensates for infrequent scooping.

Are covered litter trays better?

Usually not for the cat. Most cats prefer an open tray where they can see out and are not enclosed with the smell. Hoods suit the owner, and a cat that avoids a hooded tray is telling you something.