Measure your cat four times and get the minimum inside size of its carrier by the IATA formula, then check a carrier you own or an airline's under-seat limit against it.
Cat Carrier Size Calculator - IATA Formula and Airline Check
Measure your cat four times and get the minimum inside size of its carrier by the IATA formula, then check a carrier you own or an airline's under-seat limit against it.
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What size carrier your cat needs, from four tape measurements
Weight charts on carrier boxes guess; the airline industry measures. This cat carrier size calculator uses the formula from the IATA Live Animals Regulations, the standard airlines apply to pet containers, and turns four measurements of your cat into the minimum inside length, width and height. A cat of 18 in from nose to tail base, 5 in to the elbow, 5 in across the shoulders and 11 in tall needs at least 20.5 x 10.0 x 11.0 in inside. Add your own carrier or an airline's under-seat limit and it checks both, side by side.
Four measurements, then the optional extras
- Unit - inches or centimeters, used for every measurement on the form.
- Length A - tip of the nose to the base of the tail, cat standing.
- Elbow height B - floor to the elbow joint of a front leg.
- Width C - across the shoulders or the widest point of the body, whichever is greater.
- Standing height D - floor to the top of the head or the ear tips, whichever is higher.
- Bedding, snub nose, number of cats, age, weight - optional adjustments; bedding thickness is added to the height.
- Your carrier and the airline limit - optional, three inside sizes each.
- Read the minimum and the two checks underneath it.
Why measuring beats a weight chart
The rule behind every number here is a single sentence in the IATA regulations: each animal must have enough space to stand, sit erect, lie in a natural position and turn about normally while standing. The formula is the guidance IATA gives for reaching that, and the regulations say it "may need to be adjusted" if the cat still cannot do all four. Two cats of the same weight can differ by inches in leg length and in how tall they stand, which is exactly what a chart by pounds ignores.
The length gets half of the elbow height on top of the body because a cat lying on its side stretches its legs out. Width is twice the shoulders so there is room to turn. Height is plain standing height, plus whatever bedding lies on the floor: a 1 in pad means 1 in more headroom. Every result is an inside measurement. Product listings often give outer size, so take the wall thickness off before comparing.
More than one cat in one carrier changes only the width: C x 3 for two and C x 4 for three, with length and height worked out for the largest. Sharing is tightly limited, though. Two adults may share only if they are of comparable size, used to living together and up to 14 kg (30.9 lb) each; three only as kittens up to six months old. In the cabin each airline adds its own rule on how many pets one carrier may hold.
Minimum inside size for six example cats
The measurements below are examples, not breed averages; your own tape measure decides. The rows show how the four numbers become the three sizes for a single cat with no bedding.
| A / B / C / D (in) | Length | Width | Height | Snub-nosed |
|---|---|---|---|---|
| 14 / 4 / 4 / 9 | 16.0 in | 8.0 in | 9.0 in | 17.6 x 8.8 x 9.9 |
| 16 / 4.5 / 4.5 / 10 | 18.3 in | 9.0 in | 10.0 in | 20.1 x 9.9 x 11.0 |
| 18 / 5 / 5 / 11 | 20.5 in | 10.0 in | 11.0 in | 22.6 x 11.0 x 12.1 |
| 20 / 5.5 / 5.5 / 12 | 22.8 in | 11.0 in | 12.0 in | 25.0 x 12.1 x 13.2 |
| 22 / 6 / 6 / 13 | 25.0 in | 12.0 in | 13.0 in | 27.5 x 13.2 x 14.3 |
| 24 / 6.5 / 6.5 / 14 | 27.3 in | 13.0 in | 14.0 in | 30.0 x 14.3 x 15.4 |
Five details that change the answer
The last of those cases, side by side. One cat, 18 / 5 / 5 / 11 in, no bedding, against an under-seat limit typed in as 18 x 11 x 11 in:
| Side | Minimum for the cat | Limit typed in | Room |
|---|---|---|---|
| Length | 20.5 in (52 cm) | 18.0 in (46 cm) | short by 2.5 in (6 cm) |
| Width | 10.0 in (25 cm) | 11.0 in (28 cm) | fits |
| Height | 11.0 in (28 cm) | 11.0 in (28 cm) | fits, with nothing to spare |
Who gets the tape measure out
Owners booking a flight type in the airline's maximum and learn before the airport whether the cat can fly in the cabin at all. Owners shopping for a carrier check a listing's inside measurements against the minimum instead of trusting "fits cats up to 15 lb". Two-cat households see the width for sharing and the limits on who may share. And owners of flat-faced cats get the extra 10% worked in automatically.
Carrier sizing, asked and answered
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