Too little litter is one of the most common reasons a litter box smells, gets messy and is hard to clean. Too much just ends up on the floor. Here's how much litter to use, why depth matters, and how to measure it in your box.
QUICK ANSWER
Fill your litter box with at least 3 inches of litter. That's deep enough for clumping litter to form solid clumps before urine reaches the bottom of the box, and deep enough for your cat to dig and cover comfortably. Top it back up to 3 inches as the level drops.
In this guide:
- Why litter depth matters
- How to measure 3 inches
- How much litter for your box size
- Signs you're using too little or too much
- Topping up vs a full change
Why Litter Depth Matters
When the litter is too shallow, urine runs straight to the bottom of the box before the litter can absorb it. Instead of a solid clump you can lift out, you get a wet patch stuck to the plastic. That's what makes a box smell even right after you've cleaned it.
With at least 3 inches, clumping litter has room to do its job:
- Clumps form properly and lift out in one piece, instead of breaking apart.
- Less sticks to the box, so cleaning is quicker and the plastic holds less odor.
- Your cat can dig and cover, which most cats like to do before and after they go.
Good to know: If you use a litter box liner, depth matters even more. With at least 3 inches of litter, your cat digs in the litter, not on the liner underneath.
How to Measure 3 Inches
You don't need to guess. Stand a ruler upright in the corner of the empty box and mark the 3-inch line on the inside wall with a permanent marker. Fill to the line, and top up to it every few days.
QUICK CHECK
Push a finger straight down into the litter in the middle of the box. If you hit the bottom almost straight away, it's time to top up.
How Much Litter for Your Box Size
Here's roughly how much litter it takes to fill common box sizes to 3 inches. Most boxes taper towards the bottom, so you'll usually need a little less than this.
| Box size (L x W) | Litter for 3 inches deep |
|---|---|
| Small: 14 x 10.5 in | About 1.9 gallons (7 litres) |
| Medium: 16 x 12 in | About 2.5 gallons (9.5 litres) |
| Large: 18.5 x 15 in | About 3.6 gallons (13.5 litres) |
| X-Large: 21.75 x 16.75 in | About 4.7 gallons (18 litres) |
Not sure what size your box is? Measure the inside of the base, length and width, and use the closest row.
Signs You're Using Too Little or Too Much Litter
Too little litter:
- Clumps stick to the bottom of the box or fall apart when you lift them.
- The box smells soon after you clean it.
- You can see the bottom of the box after your cat digs.
Too much litter:
- Litter gets kicked over the sides every time your cat digs.
- You're throwing away a lot of clean litter with each clean.
What helps: Keep the level at about 3 inches. If litter still ends up on the floor, a box with higher sides or a mat outside the box usually fixes it.
Topping Up vs a Full Change
Every time you clean, a little litter goes out with the waste, so the level drops. Top it back up to 3 inches every few days. Topping up isn't the same as a full change, though. Even with daily cleaning, the whole box needs fresh litter and a wash every so often. Here's how often to change cat litter.
If your box still smells even at the right depth, read why your litter box still smells and how to fix it.
An Easier Way to Keep the Right Depth
CatSheets is a sifting litter box liner system. Instead of scooping, you lift the top perforated sheet: clean litter falls back into the box through the holes, and the waste stays on the sheet for you to toss. Because clean litter goes back into the box instead of out with the scoop, the level drops more slowly.
It works best with at least 3 inches of clumping litter in boxes up to 21.75 x 16.75 x 6.5 inches. Fine pellets and granules under 3/8 inch work too, but large pellets and extra-large crystals won't pass through the holes. Here's how sifting litter box liners work.
THE CATSHEETS METHOD
SET IT → LIFT IT → SIFT IT → TOSS IT
Shop CatSheets sifting liners (free US shipping) →
Litter Depth: Quick Answers
How many inches of litter should be in a litter box?
At least 3 inches. That's enough for clumps to form before urine reaches the bottom of the box.
Does more litter mean less smell?
Up to a point. Going from a thin layer to 3 inches makes a big difference, because urine stops pooling on the plastic. Beyond that, regular cleaning matters more than extra depth.
How often should I top up the litter?
Every few days, or whenever the level drops noticeably below 3 inches. Marking a 3-inch line inside the box makes it easy to see.
What type of litter works best?
Clumping litter is the easiest to keep clean, because waste forms solid clumps you can lift out. With CatSheets, clumping litter gives the fastest sift.
Can I use pellet litter with a sifting liner?
Only if the pieces are small. Fine pellets and granules under 3/8 inch (9.5 mm) sift through the holes. Large pellets and extra-large crystals won't.