How Much Litter to Put in a Litter Box

How to use it

1. Measure the inside of the pan, along the bottom. Litter boxes taper, so the rim is wider than the floor. Measuring at the rim will have you buying roughly a tenth more litter than the box holds. If you can't be bothered, pick the closest preset size.
2. Tell it what litter you use. This matters more than people expect. A box of clumping clay and the same box of tofu differ in weight by more than double, and they need genuinely different depths.
3. Flag anything unusual about the cat. A kitten, an arthritic senior, or an enthusiastic digger each changes the right depth, and the tool tells you which rule it applied and why.
4. Add your bag size if you want the shopping answer. You'll get how many fills a bag gives you and roughly how much litter a month you're going through.

The short answer, before the detail

For most cats and most litters, two to three inches is the honest general answer, and in a standard 17 by 13 inch pan that's somewhere between 8 and 22 lb depending entirely on what the litter is made of. But the general answer is where the advice stops everywhere else, and it's the part that costs people money. The two adjustments worth making:

• Clumping litter wants 3 to 4 inches. Urine needs to form a clump before it reaches the floor of the pan. Too shallow and the clump welds itself to the plastic, which is the single most common reason people think their litter is bad when their depth is.
• Pellets and crystals want 1 to 2 inches. Wood and paper pellets work as a single sifting layer and crumble into sawdust as they absorb. Crystals absorb and evaporate on a shallow bed you stir. Depth beyond that is litter you throw away unused.

Why this tool is different from other "how much litter" pages

Search this question and you'll get the same sentence from every result: two to three inches. It's not wrong, it's just not an answer to what people are actually asking, which is how much to buy and how much to pour.

• It answers in pounds, not inches. Your box has a size and your litter has a weight, so the pounds are calculable. As far as we can find, no other page does this arithmetic for you.
• The depth changes with the litter. Everywhere else gives one number for all eight litter types, which is wrong in both directions: it under-fills clumping clay and wastes half a bag of pellets.
• Eight litter types with their real weights, in one table. Litter is sold by weight in America and by volume in Europe, so a pack printed in both litres and kilograms is a density measurement the manufacturer made for us. That's where these numbers come from.
• It solves the ruler problem instead of naming it. One competitor writes that "not everyone has a ruler on hand when filling the box" and then leaves you there. Every result here comes with an everyday-object comparison, and the printable guide includes a true-to-size strip you cut out and stand in the pan.
• It tells you what a bag actually gives you. Fills per bag, days per bag, and pounds a month for the number of cats sharing the box.

How the maths works

There's no clever model here, which is the point. It's the volume of a box multiplied by the weight of what you're filling it with:

volume (cu ft) = length x width x depth / 1728

pounds = volume (cu ft) x density (lb per cu ft)

Everything rests on that density figure, so it's worth being clear where it comes from. Cat litter is sold by weight in the United States and by volume in Europe, which means a pack printed in both litres and kilograms is a bulk-density measurement made by the manufacturer. Reading those pairs off real products gives the weight of each litter type directly, and they agree closely within a material: three separate tofu brands all sell 6 litres at 2.5 kg, and five independent wood-pellet sellers all list 30 litres at 15 kg.

Clumping clay is the heavy one at about 56 lb per cubic foot, which lines up with the industrial spec sheet for cat-litter-grade sodium bentonite (65 lb per cubic foot uncompacted, before it's granulated for retail). At the other end, paper and tofu pellets come in near 26 lb per cubic foot, less than half. That single fact explains why the same box can weigh 25 lb or 8 lb depending only on what you poured into it.

The honest limitation: brands within a type vary by roughly 15% either way, so the tool shows a band around every figure. Walnut is the weakest number in the table. No walnut litter appears to be sold in dual units anywhere, so its density is taken from walnut-shell blasting-media specifications rather than measured off a pack, and it's flagged as estimated in the tool.

As a check the model wasn't built around: at the generic three-inch fill everyone recommends, it puts one cat on clumping clay at about 39 lb of litter a month. Published figures for that exact case run 28 to 40 lb a month. It lands inside the band without being tuned to it. Which raises the finding worth knowing. At the 3.5 inches clumping clay actually wants, that same cat uses closer to 45 lb a month. The gap is real, not an error. It's why your bag runs out faster than the internet promised, and it's the trade you make for clumps that lift cleanly.

Three worked examples

One cat, standard box, clumping clay

A 17 by 13 inch pan at 3.5 inches takes about 25 lb, which is most of a 40 lb bag. That bag gives you roughly one and a half full changes. With a full change every two to four weeks plus what leaves with the clumps, budget on somewhere between 31 and 59 lb a month. This is the case people find shocking, and it's usually the moment they discover they've been filling too shallow rather than buying too much.

The same box, switched to tofu

Tofu clumps at 2.5 inches and weighs a fraction of clay, so the same pan takes about 8 lb. If you've been lugging 40 lb bags up a flight of stairs, that difference is the actual selling point of plant litters, more than the flushability. Whether it suits your cat is a separate question, covered in clumping versus non-clumping litter.

A kitten pan for a ten-week-old

A 14 by 10 inch tray, capped at 1.5 inches because a kitten needs to climb in without wading, comes out at under 7 lb. Worth pairing with a non-clumping litter at that age: kittens under about four months sometimes eat litter, and clumping clay is the type to postpone. Once they're using it reliably, litter training covers the rest.

Frequently asked questions

How deep should cat litter be?

Two to three inches for most litters, three to four for clumping. The reason clumping is deeper is mechanical rather than a preference: urine has to be fully absorbed into a clump before it hits the bottom of the pan, and a shallow bed lets it reach the plastic and stick there. Pellets and crystals go the other way, at one to two inches, because they work as a shallow layer and extra depth does nothing but sit there.

How much litter in a litter box, in pounds?

For a standard 17 by 13 inch pan: roughly 25 lb of clumping clay, 17 lb of walnut, 15 lb of corn, 8 lb of tofu or non-clumping clay, 6 lb of wood pellets, and about 5 lb of crystals or paper pellets. The spread is enormous because it's driven by what the litter is made of, not by the box. Put your own dimensions into the calculator above for your exact figure.

Can you put too much litter in a litter box?

Yes, and it's a more common mistake than under-filling. Past about four inches many cats feel unsteady, sink as they dig, and start flinging litter over the side trying to get purchase. Some stop using the box altogether. If you're dealing with litter all over the floor, adding depth is the wrong instinct. The fix is a higher-sided or top-entry box with slightly less litter in it.

How long does a 40 lb bag of cat litter last?

For one cat on clumping clay in a standard box, roughly three to four weeks. The bag holds about one and a half full changes, and the rest goes on topping up after scooping. Cut that roughly in half for each extra cat sharing the box. With a light litter like tofu or crystals, a bag covers far more fills but the bags are smaller, so cost per month is the fairer comparison than bag life.

How much litter should I put in an automatic litter box?

Fill to the marked line and no further, whatever depth that turns out to be. Over-filling is the most common cause of a jammed rake or globe and it usually isn't covered by the warranty. These boxes are also fussier about litter type than open pans, and some need clumping clay specifically, some come with their own crystals. Dr. Anand's guide to the best automatic litter boxes covers which machines take which litter.

Should I top up the litter after scooping, or wait for a full change?

Top up. Every clump you scoop takes litter out with it, so a box that started at three inches is measurably shallower a week later, and that's how a clumping box quietly falls below the depth it needs. Add a handful after scooping to hold the level, and keep the full change on its own schedule. See how often to change cat litter for what that schedule should be.

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Litter and boxes that match your answer

Once you know the depth and the weight, the tool suggests a few things that suit it: a hard-clumping clay and a high-sided pan if you're filling deep, a pellet system if you're filling shallow, a low-entry box for a senior. For the full shortlists, see Dr. Anand's guides to the best cat litter, the best cat litter boxes, and the best automatic litter boxes.

Methodology & sources

Weight is box volume times bulk density, with no fitted coefficients. Densities are read from retail packs sold in both litres and kilograms, cross-checked against spec sheets for the same raw material, and are listed with their evidence in the tool's fixtures file. Recommended depths follow the two-to-three-inch consensus across the major litter brands and retailers, adjusted per material for the mechanical reasons described above. An automated fixture test runs on every site build: it asserts every litter type's weight at a standard box, that the kitten and senior depth caps bind on all eight types, that the digger adjustment never breaches its two-inch floor, that metric and imperial inputs agree, that bag arithmetic round-trips, and that the monthly estimate for one cat on clay lands inside the published 28 to 40 lb band.

• NATIONAL CAT 10 granular bentonite for cat litter, technical data sheet, bulk density 65 lb/ft³ uncompacted (bentonite.com)
• Dual-unit retail packs used for density: Catsan Hygiene 10 L / 4.8 kg; Versele-Laga Premium Silica 5 L / 2.3 kg; duvoplus maize 10 kg / 16.37 L; Purrby, WEELITTER and Michu tofu 6 L / 2.5 kg; wood pellets 30 L / 15 kg; Purecat paper 10 L / 3.97 kg
• Chewy: How Much Cat Litter Should I Use? (2–3 inch baseline, automatic-box fill lines)
• Litter-Robot: How Much Cat Litter Should You Use? (published consumption of 7–10 lb per week for one cat)
• World's Best Cat Litter: Are You Using Too Much Cat Litter? (signs of over-filling)

Reviewed annually for citation currency and for new litter categories entering the market. About Dr. Anand · Last reviewed August 24, 2026.

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