Four measurements of your pet, taken standing and relaxed, and you have the container size an airline will accept. The number that matters is the space inside the box — and that is not the number printed on the box.
What size airline crate does your pet need?
Airline containers are sized with four measurements, not by breed or by body weight. Take them with your pet standing relaxed on the floor. The result is the space your pet needs inside the box — which is not the number printed on the box.
| Measurement | What to measure | How it is used |
|---|---|---|
| A | Nose to the base of the tail, not the tip of the tail. | Sets the base of the length. |
| B | Floor to the point of the elbow, front leg. | Half of it is added to the length, so the pet can stand without crouching. |
| C | The widest point of the body — shoulders or chest, whichever is wider. | Doubled for the width. |
| D | Floor to the top of the head, or the tips of the ears if they are higher. | Sets the height, plus room for bedding. |
| Formula | Result |
|---|---|
| Internal length | A + 0.5 × B |
| Internal width (one pet) | C × 2 |
| Internal width (each extra pet) | + 1 × C |
| Internal height | D + 3 cm of bedding |
| Flat-faced breeds | Everything above × 1.10 |
Container requirements come from the IATA live animals regulations, which is what airlines actually check against at the gate.
What that works out to for common sizes
Typical measurements, so you can sanity-check your own. The outside figures include about 2.5 cm of wall and latch per side — that is the space a box loses between what it says and what your pet gets.
| Pet | Inside L × W × H | Shop for at least |
|---|---|---|
| Small catA 40 · B 12 · C 14 · D 30 cm | 46 × 28 × 33 cm | 51 × 33 × 38 cm |
| Large catA 48 · B 14 · C 16 · D 34 cm | 55 × 32 × 37 cm | 60 × 37 × 42 cm |
| Small dogA 45 · B 16 · C 18 · D 36 cm | 53 × 36 × 39 cm | 58 × 41 × 44 cm |
| Medium dogA 60 · B 20 · C 24 · D 50 cm | 70 × 48 × 53 cm | 75 × 53 × 58 cm |
| Large dogA 80 · B 26 · C 30 · D 65 cm | 93 × 60 × 68 cm | 98 × 65 × 73 cm |
Three things that catch people out
| Point | Why it matters |
|---|---|
| You calculate the inside; you buy the outside | A box listed as 70 cm long typically gives your pet closer to 60 cm once the walls, the door and the latch are accounted for. If you size on the outside number you will buy one that is too small — and airline staff measure the pet in the box, not the box on its own. |
| Bigger is not automatically cheaper or safer | Carriers charge by the greater of actual weight and volumetric weight, which is length × width × height divided by roughly 5,000 to 6,000. Going up a size can push the shipment into a higher charge band for no benefit. |
| Flat-faced breeds are a rules problem, not a size problem | Short-nosed dogs and cats need the extra 10%, but several airlines restrict or refuse them outright in the hold, and most impose summer embargoes. Check with the airline before you buy anything. |
Airline rules differ on weight caps, breed restrictions and carrier types. Terminal staff apply the live animals regulations, but each airline adds its own conditions — confirm with the specific carrier you are flying.
Why this uses measurements and not a breed chart
Search for crate sizes and you will find charts that map breeds to box numbers. They are a useful starting point and a bad final answer, because the range inside a single breed is enormous — two labradors can differ by 10 cm in length and 8 kg in weight. What the airline measures at the gate is your pet in the box, standing. So that is what this calculator sizes for: the pet in front of you.
The container is the easy part
Getting the size right is necessary and nowhere near sufficient. Carriers impose weight caps that combine the pet and the container, restrict or refuse flat-faced breeds in the hold, and apply summer embargoes on top. Space for animals on a given flight is limited and sells out long before passenger seats do. Sort out whether your pet can fly on your chosen airline, and on which dates, before you spend anything on a box.
Why there is no car section here
Travel crates for cars have no equivalent international standard, and the crash testing that does exist is voluntary. We could invent a formula that looked authoritative, and it would be worthless — so this tool stays with air travel, where the IATA live animals regulations give a real answer. For a car, the honest guidance is a crate that does not move under hard braking, and one that has passed a recognised crash test.