How many litter boxes do your cats need, and how big? The count per cat and floor, the minimum box length from your cat's size, and the quarts of litter that fill them.
Litter Box Calculator - How Many Boxes, Size and Litter
How many litter boxes do your cats need, and how big? The count per cat and floor, the minimum box length from your cat's size, and the quarts of litter that fill them.
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How many litter boxes, how big, and how much litter
Two boxes for one cat, three for two, and never fewer than one on each floor: that is the count the litter box calculator returns, following the AAFP and ISFM house-soiling guidelines. It also turns your cat's body length into a minimum box length, checks the box you already own, and works out how many quarts of litter fill every box at the recommended depth. A cat measuring 18 in from nose to tail base needs a box at least 27 in long.
Measuring the cat and filling in the form
- Number of cats - every cat that uses the boxes, from 1 to 20.
- Unit - inches or centimeters. The same unit is used for the cat, the box and the litter depth.
- Cat length - nose to the base of the tail, tail left out. Measure the largest cat while it stretches or lies flat.
- Floors - optional, levels of the home the cats can reach. Empty means one.
- Senior or arthritic cat - optional. A yes adds advice on a low entry.
- Box length and width - optional, inside measurements of the box you have or plan to buy.
- Litter depth - optional. Empty uses the guideline minimum of 1.25 in (3 cm).
- Weight of one quart of litter - optional, in ounces from a kitchen scale, to get pounds per fill.
- Read the result - box count, minimum length, litter volume and the upkeep table.
Eight homes, eight litter box setups
A single cat in an apartment
Situation:1 cat, 18 in, 1 floorResult: 2 boxes in two separate spots, each at least 27.0 in (69 cm) long.
Two cats, the larger one 20 in
Situation:2 cats, 20 inResult: 3 boxes, minimum length 30.0 in (76 cm).
One cat in a three-story house
Situation:1 cat, 3 floorsResult: 3 boxes, because one per floor beats the plus-one count of 2.
Four cats on two floors
Situation:4 cats, 2 floorsResult: 5 boxes, spread over both floors, and 5 scoops a day at the least.
A long cat
Situation:1 cat, 24 inResult: minimum length 36.0 in (91 cm), longer than the 34 x 15 in box adult cats preferred in the study the guideline cites.
Checking a standard box for two cats
Situation:2 cats, 18 in, box 24 x 16 in, depth emptyResult: too short by 3.0 in; 8.3 qt (7.9 L) of litter per box, 24.9 qt (23.6 L) for all 3.
Litter by weight for a bigger box
Situation:1 cat, 18 in, box 34 x 15 in, 2 in deep, 24 oz per quartResult: 17.7 qt per box, 35.3 qt for both, about 53.0 lb of litter to fill them.
The same check in centimeters
Situation:1 cat, 46 cm, box 86 x 39 cmResult: minimum 27.2 in (69 cm), the box passes, and 10.1 L of litter fills it at 3 cm.
Minimum box length for each cat length
The rule is one multiplication: 1.5 times the cat from nose to tail base. The table shows where common cat lengths land.
| Cat, nose to tail base | Minimum box length |
|---|---|
| 12 in (30 cm) | 18.0 in (46 cm) |
| 14 in (36 cm) | 21.0 in (53 cm) |
| 16 in (41 cm) | 24.0 in (61 cm) |
| 18 in (46 cm) | 27.0 in (69 cm) |
| 20 in (51 cm) | 30.0 in (76 cm) |
| 22 in (56 cm) | 33.0 in (84 cm) |
| 24 in (61 cm) | 36.0 in (91 cm) |
Quarts of litter per box at three depths
Volume is length times width times depth, and one US quart is 57.75 cubic inches. The first depth column is the guideline minimum; the others show how fast a deeper fill adds up.
| Inside size | 1.25 in deep | 2 in deep | 3 in deep |
|---|---|---|---|
| 18 x 14 in | 5.5 qt (5.2 L) | 8.7 qt (8.3 L) | 13.1 qt (12.4 L) |
| 20 x 16 in | 6.9 qt (6.6 L) | 11.1 qt (10.5 L) | 16.6 qt (15.7 L) |
| 24 x 18 in | 9.4 qt (8.8 L) | 15.0 qt (14.2 L) | 22.4 qt (21.2 L) |
| 30 x 20 in | 13.0 qt (12.3 L) | 20.8 qt (19.7 L) | 31.2 qt (29.5 L) |
| 34 x 15 in | 11.0 qt (10.4 L) | 17.7 qt (16.7 L) | 26.5 qt (25.1 L) |
| 36 x 24 in | 18.7 qt (17.7 L) | 29.9 qt (28.3 L) | 44.9 qt (42.5 L) |
Where do the rules come from? The count, the 1.5 rule, the 1.25 in minimum depth and the upkeep schedule are all in the AAFP and ISFM Guidelines for Diagnosing and Solving House-Soiling Behavior in Cats. The same document is candid that the plus-one count is "not an absolute requirement": cats that get along may share, and cats that do not need separate stations, which can push the number up.
Litter box questions owners type in
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