CollarPassIATA sets the floor for pet crates; airlines set the ceiling. The floor is Container Requirement 1 of the IATA Live Animals Regulations, Edition 52, January 2026, which fixes the minimum internal size, ventilation area, mesh gauge, fasteners and water access. Carriers add their own limits, and the stricter of the two decides whether your crate is accepted.
The gap between the two is where rejections happen. A crate can be legal by IATA and still be refused because it is soft-sided on a route that only takes rigid kennels, because its wheels were left on, or because the pet's ears touch the roof. This guide covers the measurements and the specific failures, using IATA and two airlines that publish their rules in detail.
Sources: IATA Traveler's Pet Corner and IATA Container Requirement 1 — checked November 11, 2026.
Quick answer
- Measure the animal, not the old crate: length A + half the elbow height B, width twice the shoulder width C, height D plus bedding.
- Snub-nosed breeds need 10% more internal volume than the formula gives.
- Ventilation must cover at least 16% of the total surface of the four sides, and it must be on all four sides.
- Openings must be nose- and paw-proof: no more than 25 mm square for dogs, 19 mm for cats.
- Wheels come off, plastic clips are not enough, and the door pins must engage at least 1.6 cm.
- Cabin and checked baggage are two different rule sets. Hard-sided kennels are often barred from the cabin; soft-sided bags are often barred from the hold.
Sources: IATA Container Requirement 1 — checked November 11, 2026.
Measure the animal first
IATA uses four measurements, taken standing: A is nose to tail base, B is ground to elbow, C is shoulder width or the widest point, and D is the floor to the top of the head or ear tips, whichever is higher. The minimum internal dimensions are length A plus half of B, width C times two, and height D plus the depth of the bedding.
For two compatible animals the width becomes C times three; for three, C times four. Only two adults of comparable size, up to 14 kg each, may share a container; anything over 14 kg travels alone. Puppies and kittens may share if under six months, no more than 14 kg each, and no more than three.
Height fails most often: a dog that can stand but not lift its head, or whose ears brush the roof, fails the requirement to stand erect. Measure the tallest posture the animal uses, then add bedding.
Sources: IATA Container Requirement 1 — checked November 11, 2026.
Ventilation: the 16% rule
The total ventilated area must be at least 16% of the total surface of the four sides. Ventilation must run along all four sides, with side and back openings in the upper two-thirds. The whole of one end, which can be the door, must be welded wire mesh.
Mesh must be 2.5 mm or more for dogs and 2.0 mm for cats. Openings must be nose- and paw-proof: 25 mm square maximum for dogs, 19 mm for cats. Containers made entirely of welded mesh, or any other wire mesh, are not acceptable.
Obstruction is the quiet killer: a "Live Animals" label, crate cover, tarp or jacket over the crate can block the openings, and airlines refuse plastic or fabric coverings over the ventilation.
Sources: IATA Container Requirement 1 — checked November 11, 2026.
Construction details that get checked
The container must be rigid: fibreglass, metal, rigid plastic, welded wire mesh, solid wood or plywood. The interior must be smooth, the floor solid and leak-proof, and the roof solid, although roof mesh is allowed if the structure stays intact.
Fasteners matter. A plastic crate assembled from a top and a bottom must be bolted, with metal nuts and bolts in every hole rather than plastic clips alone. Wooden sides must be 12 mm thick for dogs and 6 mm for cats. Door pins must engage at least 1.6 cm. Spacers are required along both long sides and the back, and forklift spacers at least 5 cm high once the loaded container exceeds 60 kg.
Water access is part of the standard: an open water container fixed inside, reachable from outside without opening the door. Water bottles do not count.
Sources: IATA Container Requirement 1 — checked November 11, 2026.
What airlines actually reject
Alaska Airlines publishes both lists, and they are representative. In the baggage compartment it refuses carriers that are collapsible, soft-sided, cardboard, wicker, mesh or wire, or that have a snap-top; carriers built with zip ties, duct tape or rubber bands; carriers with wheels attached; carriers whose top and bottom are held only by twist, slide or snap fasteners; carriers with a plastic or locked door; and carriers covered by a tarp or fabric that blocks ventilation.
Air New Zealand publishes the same kind of list from the other direction: ventilation holes only in the upper half of three sides, excluding the door; a door covered with welded mesh; a spacer bar on three sides; two fasteners per side once a carrier is longer than 60 cm; cable ties on all four corners of the door; and no cable ties threaded through ventilation holes or cut short.
Both airlines also impose ceilings IATA does not: Alaska caps pet and carrier at 150 lb (68 kg) combined, refuses kennels over 28 inches inside Hawaii, and publishes checked sizes from 21 x 16 x 15 to 40 x 27 x 30 inches.
Sources: Alaska Airlines baggage compartment rules, Air New Zealand pet carriers, and IATA — checked November 11, 2026.
Cabin and hold are different rule sets
In the cabin, IATA relaxes several requirements: the container need not be rigid, spacers are not required, and food and water containers are not needed. It must still carry a "Live Animals" label without blocking ventilation, fit under the seat in front, and let the animal sit, stand, turn and lie down.
Airlines narrow that further. Alaska allows soft-sided carriers up to 17 x 11 x 9.5 inches in the cabin, no hard-sided kennels, and requires the carrier to be clean, leak-proof with absorbent non-shredded bedding, escape-proof, adequately ventilated and free of tears or cracks.
In the hold the reverse applies: soft-sided and collapsible carriers are refused, and the rigid rules above apply in full. A carrier bought for the cabin is almost never legal for the hold.
Sources: IATA in-cabin guidance, Alaska Airlines cabin rules, and IATA Container Requirement 1 — checked November 11, 2026.
Breeds, heat and refusals you cannot argue with
Snub-nosed breeds need a container 10% larger than the formula produces, and IATA tells operators to stow them as far as practical from other loads so they get the most air. Many airlines go further and refuse brachycephalic dogs and cats in the hold entirely; Alaska lists Boston terriers, boxers, bulldogs, pugs, shih tzus, Persians and Himalayans among the refused breeds, while still allowing them in the cabin if the carrier fits under the seat.
Other hard limits: no animal under eight weeks, no unweaned animals, no females with suckling young, no shipment in the last third of pregnancy, and no flight within seven days of giving birth. IATA advises against sedation, and carriers may refuse a sedated animal. Temperature embargoes can stop an otherwise perfect booking.
Sources: IATA Container Requirement 1, Alaska Airlines baggage rules, and IATA in-cabin guidance — checked November 11, 2026.
A ten-minute check before you buy
Measure the animal standing, add bedding to the height, apply the formula, then add 10% for a flat-faced breed. Compare that with the internal dimensions printed on the crate, not the external ones. Check the openings against 25 mm and 19 mm, the bolts at every hole, pins that engage 1.6 cm, no wheels, and a water bowl reachable from outside.
Then read the operating airline's page for your route and fare: the rules above are the minimum, not the contract, and the stricter carrier applies on a two-airline itinerary. The international pet travel checklist puts the crate step in sequence with the documents, and pricing shows what a dated plan costs.
Sources: IATA, Alaska Airlines cabin rules, and Air New Zealand — checked November 11, 2026.
