Pet Carrier Sizes and Airline Rules
Size a pet carrier from your pet's length, height and width; for the cabin, Delta suggests a soft-sided carrier no larger than 18 x 11 x 11 inches.
By Jennifer HunterContributing writer.
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The short answer
A carrier fits when your pet can stand, sit up straight, turn around and lie down in a natural position inside it. Measure your pet first, then compare the result with the inside dimensions of the carrier, not the outside. If you plan to fly with your pet in the cabin, the airline's under-seat limit comes first, and the pet must still fit comfortably inside that size.
How to measure your pet
IATA, the airline trade body, publishes the formula airlines use for travel containers. Take four measurements of your pet, standing:
- A: length from the tip of the nose to the base of the tail.
- B: height from the ground to the elbow joint.
- C: width across the shoulders or the widest point, whichever is greater.
- D: height from the floor to the top of the head or the ear tip, whichever is higher.
Then work out the minimum inside size:
| Carrier dimension | Formula |
|---|---|
| Length | A + half of B |
| Width | C x 2 |
| Height | D + the height of any bedding |
IATA adds that snub-nosed breeds need a container about 10% larger. Measure the larger animal if two pets will share.
Example: a cat that measures 18 inches nose to tail with a 6 inch elbow height needs at least 21 inches of inside length (18 + 3). That is longer than many cabin carriers, which is why the formula matters mainly for cargo travel and for road trips, while cabin travel is limited by the seat.
Airline approved carrier size
There is no single airline approved size. Each airline sets its own limit, and it can change with the aircraft. Delta, for example:
- Recommends a soft-sided kennel no larger than 18 x 11 x 11 inches, which it says fits most of its aircraft, and points to its aircraft pages for the exact space on your flight.
- Requires the kennel to fit fully under the seat in front of you.
- Requires your pet to move around comfortably without touching or sticking out past the sides.
- Asks for a leak-proof carrier with ventilation on three sides (four for international trips).
- Allows generally one pet per kennel, with narrow exceptions for young animals.
Check the airline's own pet page for each flight before you buy, because a carrier that fits one airline may not fit another.
Soft vs hard pet carriers
| Soft-sided | Hard-sided | |
|---|---|---|
| Cabin travel | Flexes to fit under a seat; the type Delta recommends | Rigid, so it must already fit the under-seat space |
| Strength | Lighter and easier to carry | Holds its shape and protects better against bumps |
| Cleaning | Fabric; check whether it is washable | Wipes down easily |
| Fits | Small, calm pets, flights, short trips | Car travel, vet visits, pets that chew or scratch |
Of the 245 pet carriers listed on Wiki Shopping, 83 state they are soft-sided and 19 hard-sided; the rest do not say.
How we count
The measuring formula is IATA's and the cabin rules are Delta's, both linked under Sources. The example is our own arithmetic with that formula. Carrier counts come from our database on October 26, 2026 and change as listings are added or removed.
Shopping on Wiki Shopping
Carriers sit in the pet supplies department. Read the inside dimensions on each listing and compare them with your pet's measurements.