Stand in the pet aisle for long enough and you will hear both arguments. Covered boxes are better because cats want privacy and they keep the smell in. Open boxes are better because cats feel trapped in a hood and a covered box is a gas chamber of ammonia. Both sides say it with total confidence. Both sides are mostly wrong, and the research explains why.
Two studies have actually put boxes in front of cats and counted what they used. Read together, they point at a variable almost nobody argues about.
The short version
- In a 27-cat study, 70% showed no preference at all between a covered and an uncovered box. 15% preferred covered, 15% preferred uncovered.
- A later set of trials found a preference for covered boxes only when the covered box was 17% larger. With equal floor area the difference was not significant.
- Put together: the lid is not the variable. Floor area is. Covered boxes just tend to be bigger.
- The size rule that matters: the box should be about 1.5 times the length of your cat, nose to base of tail.
- Cleaning frequency and litter type beat box design. One cat in the study avoided the covered box until the litter was swapped to an unscented brand, then used it happily.
On this page
What the two studies found
The first is the one usually quoted. Twenty-seven healthy cats, aged three months to fifteen years, were given exclusive access to two boxes side by side, one covered and one uncovered, for fourteen days. The positions were swapped on day eight so that location could not be mistaken for preference.
That result is usually reported as “cats do not care about lids”, and for most cats that is fair. But a second piece of work complicates it usefully. Two four-week trials, with thirteen cats and then twelve, looked specifically at where cats chose to defecate.
| Study | Setup | Result |
|---|---|---|
| 27 cats, 14 days | Covered and uncovered side by side, positions swapped midway | No overall preference. 15% covered, 15% uncovered, 70% no preference |
| 13 cats, 4 weeks | Covered and uncovered with equal floor area | Slight lean towards covered, not significant at the usual 5% threshold (P = 0.085) |
| 12 cats, 4 weeks | Covered box 17% larger than uncovered | Significant preference for the covered box (P = 0.011) |
The authors’ own conclusion is careful: cats may prefer commercially available covered boxes, if those boxes have a larger surface area.
Why size was the real variable
Line the three results up and the pattern is hard to miss. Equal floor area, no meaningful preference. More floor area, clear preference. The lid changed in both cases. The thing that changed the result was the space.
This makes sense from the cat’s side. A cat using a tray properly turns around, digs, positions, and covers afterwards. All of that needs room. A hood does not stop any of it. A box too small to turn around in stops all of it, which is why cats in undersized trays often stand with their front feet in and their back end out, or stop covering, or start going just beside the box.
How to measure your own cat
The working rule from the research literature is that the box should be about one and a half times the length of the cat, measured from the nose to the base of the tail, not including the tail itself.
- Measure your cat while she is lying stretched out. Nose to where the tail begins. A tape measure alongside her while she sleeps is easier than trying to hold her still.
- Multiply by 1.5. A 45cm cat wants a box with an internal length of roughly 68cm.
- Compare that with your actual tray. Most standard supermarket trays are 40 to 50cm long. For an average adult cat that is undersized, and for a large cat it is considerably undersized.
- If nothing in the shop is big enough, stop shopping in the pet aisle. A plastic under-bed storage box with one side cut down is the standard fix, costs less, and is usually the right size.
That last point is the one experienced cat owners tend to arrive at on their own. The pet industry sells trays sized for the shelf, not for the cat.
What beats box type entirely
Even a perfectly chosen box loses to these, so fix them first.
| Factor | What to do |
|---|---|
| Cleaning frequency | Scoop at least once a day. This came up in the research as more important than box style. |
| Litter type | Unscented, fine-grained, sand-like. Scent is added for humans, not cats. |
| Number of boxes | The standard guidance is one per cat plus one spare, in different locations rather than in a row. |
| Location | Quiet, not next to the washing machine, not in a dead end where another animal can block the exit. |
| Entry height | Low enough for an older or stiff cat to step into without climbing. |
The litter point deserves emphasis because of a detail in the 27-cat study. One cat who had been avoiding the covered box started using it once the litter was changed to a non-scented brand. The owner would reasonably have concluded the cat hated hoods. The cat hated the smell.
Entry height matters more than people expect in older cats. A cat with sore joints will avoid a tray she has to climb into, and the avoidance looks exactly like a preference problem. If your cat has also stopped jumping onto surfaces she used to, read what reduced jumping usually means, because the two often appear together.
When the lid does matter
Thirty percent of the cats in the first study did have a preference. Individual cats are not averages, so the lid matters in a few specific situations.
If your cat is one of the 15% who prefer open. Some cats dislike the reduced visibility, particularly nervous cats or those in a multi-cat house where being cornered is a real risk. If she uses an open tray reliably and avoids the hooded one, believe her.
In multi-cat households. A hood creates a single exit, and a cat who has been ambushed leaving a box remembers it. Open trays with sightlines are usually the safer default where cats are not entirely at ease with each other.
If she sprays or goes high. Some cats urinate standing rather than squatting, and an open tray simply cannot contain that. A high-sided open box, or a hood, is a practical answer.
What to do
- Measure the cat, then the tray. If the tray is under 1.5 times her body length, size is your problem and the lid is a distraction.
- Switch to unscented litter if you have not already, and give it a fortnight before judging anything else.
- Scoop daily. Not most days.
- Run a two-box test. Put both types side by side, swap their positions after a week so you are measuring the box and not the spot, and watch which she uses. This is exactly what the researchers did and it works at home.
- Add boxes before you add gadgets. One per cat plus one, spread around the house, solves more problems than any single purchase.
The bottom line
Most cats have no opinion about lids. What the evidence actually shows is a preference for room, which covered boxes sometimes deliver by accident because they tend to be larger. Measure your cat, buy the biggest tray that fits the space, keep it clean and unscented, and let your own cat settle the lid question by using one or the other.
Sources
- Grigg EK, Pick L, Nibblett B. Journal of Feline Medicine and Surgery, 2013. Litter box preference in domestic cats: covered versus uncovered. 27 cats over 14 days.
- Field assessment in single-housed cats of litter box type preferences for defecation, 2018. Two four-week trials with 13 and 12 cats, comparing equal and unequal surface areas.
