🐈‍⬛ Litter Box Calculator

Enter your number of cats to see the commonly recommended number of litter boxes (one per cat, plus one extra), and estimate litter volume needed.

Number of Cats

Litter Depth (in)

Box Floor Area (sq in)

One box per cat plus one, then a fill volume

The box count is the n+1 rule veterinary behaviourists quote, and the litter figure is the volume needed to fill every box to the depth you set:

boxes         = cats + 1
cu in per box = floor area × depth
quarts        = cu in / 57.75

Two cats need three boxes. A 360 sq in floor (a 24 × 15 in box) at 3 in deep holds 1,080 cubic inches, or 18.7 quarts, so filling all three takes 56.1 quarts. At 2 in deep the same three take 37.4.

Getting the inputs right

Floor area is length × width in inches, measured inside the base. Common sizes run 300 to 450 sq in; a box wants to be about one and a half times your cat's length, nose to tail base.
Depth accepts 1 to 6 in. Two to three is usual: clumping litter needs enough depth for a clump to form clear of the base, and beyond three is mostly waste.
This is a fill, not a monthly supply - with clumping litter you scoop and top up, so ongoing use is far lower.
Bags are sold by weight, not volume, and quarts convert to pounds only with that litter's density.

Spread the boxes across separate rooms; the count only helps if a cat can reach one without passing another cat. A cat that suddenly stops using the box, strains, or passes blood needs a vet appointment rather than a bigger box - and a male cat straining without producing urine is an emergency, not something to watch overnight.

Frequently asked questions

How many litter boxes do I need for 2 cats?

Three, following the one-per-cat-plus-one rule. The spare matters most where one cat guards a box and another then starts going elsewhere.

How deep should cat litter be?

Two to three inches for clumping litter, which is what the tool defaults to. Shallower and clumps stick to the base; deeper mostly gets kicked out.

How many quarts of litter fill a standard box?

About 18.7 quarts for a 24 by 15 inch box at three inches deep, and 56.1 quarts to fill three of them. That is a one-off first fill; after it you scoop and top up, so later bags go much further.