Pet Carriers Airline Approved: 2026 Size Limits, Fees and Rules by Airline

An airline-approved pet carrier is a leak-proof, ventilated carrier small enough to fit fully under the seat in front of you, with room for your cat or dog to stand and turn around inside. As of September 2026, Delta Air Lines, American Airlines and United Airlines publish a soft-sided maximum of 18 x 11 x 11 inches, and Southwest Airlines lists 18 x 10.5 x 10 inches. There is no universal size, so always check your airline and your aircraft before buying a carrier.

This guide compares the published limits from each airline's own pages, flags the places where sources disagree, and walks through how to size a carrier to both the seat and your pet. It is written by the editorial team at Animal Passport. We cover animal identification and movement, and we point out below where airline pet rules differ from identity records like ours.

What does “airline approved” actually mean for a pet carrier?

“Airline approved” is a retail label, not a formal certification. None of the airline pages reviewed for this article (Delta, American, Southwest) certifies or endorses specific retail carrier brands. Instead, each airline publishes maximum dimensions and construction rules, and gate or check-in agents decide whether your carrier meets them on the day you fly.

Delta Air Lines states in its 2026 pet travel overview that “the maximum in-cabin kennel dimensions are determined by the aircraft dimensions of your flight, as the under-seat space varies by aircraft.” In practice, a carrier marketed as airline approved is one built to fit the most common limit (about 18 x 11 x 11 inches). It can still be too tall for a particular seat or aircraft.

The one exception is Southwest Airlines, which sells its own branded pet carrier. Southwest's help center lists that carrier at 15 x 10 x 10 inches, smaller than its general 18 x 10.5 x 10 inch limit.

Airline-approved pet carrier sizes by airline (2026 comparison)

The table below summarizes the in-cabin carrier limits and fees published by four major United States airlines, checked in September 2026. Dimensions are length x width x height in inches.

Where the sources disagree

Southwest's published numbers have changed. A Southwest Airlines media-site article, “Flying with Felines,” gives maximum carrier dimensions of 18.5 inches long x 8.5 inches high x 13.5 inches wide and a $95 pet fare. Southwest's current help center lists 18 x 10.5 x 10 inches. Go by the current help center figure, and treat the older article as out of date.

Delta's pet travel overview does not publish a separate hard-sided in-cabin maximum. The independent guide Borderless Moves also noted this gap in 2026. Delta does say that both soft- and hard-sided kennels must fit fully under the seat, so ask Delta Reservations before buying a hard-sided carrier for a Delta flight.

We could not load United Airlines' official in-cabin pet page when researching this article. United's figures in the table come from CabinPets, a third-party tracker that cites United's pet policy. Check them on united.com before you buy.

What features does every airline-approved pet carrier need?

The airlines word their rules differently, but they converge on the same core requirements:

• Fits fully under the seat in front of you. Delta, American and Southwest all require the carrier to stay stowed under the forward seat for the entire flight.
• Leak-proof. Delta and Southwest both specify leak-proof carriers, and American requires water-repellent material.
• Ventilated. Delta requires ventilation openings on 3 sides for domestic travel and 4 sides for international travel on soft-sided kennels. American requires nylon mesh ventilation on 3 or more sides.
• Room to move. Delta says your pet must be able to move around without touching or sticking out from the sides. Southwest says the pet, including head and tail, must be completely inside and able to stand up and move around with ease.
• Secure and padded. American Airlines requires soft-sided carriers to be secure and padded.
• Designed for pets. Southwest requires carriers to be “specifically designed as pet carriers,” which rules out repurposed bags.

Soft-sided vs hard-sided: which is better for the cabin?

Soft-sided carriers are the safer choice for in-cabin travel. American Airlines recommends them, saying soft-sided collapsible kennels “can be slightly larger but still need to fit under the seat without having to excessively collapse the kennel.” Southwest also recommends soft-sided carriers, because under-seat space varies by seat type and location, including aisle seats.

Hard-sided carriers get stricter and less consistent limits. On American Airlines they must be no larger than 16 x 12 x 8 inches on regional American Eagle aircraft, much smaller than the 19 x 13 x 9 inches allowed on mainline jets. American also says non-collapsible kennels cannot exceed the under-seat dimensions of any aircraft in your journey. That means one regional connecting flight can set the limit for the whole trip.

How do you size a carrier to your pet?

The airline sets the maximum size of the carrier. Your pet's body sets the minimum. The International Air Transport Association (IATA) publishes a sizing formula on its Traveler's Pet Corner page, based on its Live Animals Regulations (LAR) Container Requirement 1 for cats and dogs (2026 edition). Measure your pet standing:

• A = length from tip of nose to base of tail
• B = height from ground to elbow joint
• C = width across the shoulders or widest point
• D = height from floor to top of head or ear tip, whichever is higher

IATA's minimum internal container dimensions for one animal are length = A + ½ B, width = C x 2 and height = D + bedding, and snub-nosed breeds need a container 10% larger. These are internal measurements. IATA's formula is mainly used for pets traveling in the hold or as cargo, but it is still a good check on whether your pet will be comfortable in a cabin carrier.

If your pet's minimum carrier is larger than your airline's under-seat maximum, the pet is not a candidate for cabin travel on that flight. A larger carrier will not change that.

How to choose an airline-approved pet carrier: 8 steps

1. Confirm your route allows cabin pets. Delta does not allow in-cabin pets to or from destinations including Hawaii, the United Kingdom, Australia and New Zealand. Southwest's Contract of Carriage says it accepts no pets on international itineraries. American Airlines does not allow carry-on pets on trans-Atlantic or trans-Pacific trips.
2. Identify every aircraft on your itinerary. Under-seat space differs by aircraft and cabin. American's A321XLR, 777 and 787 aircraft do not allow pets in premium cabins because there is no under-seat storage.
3. Measure your pet using the IATA A-B-C-D method above.
4. Measure the carrier's outside dimensions, including pockets, frames and bulges, not just the size on the label.
5. Compare against the strictest segment. Use the smallest limit across all flights, especially if a regional jet is involved.
6. Reserve your pet's spot early. Delta allows up to 4 pets in Delta Comfort and Delta Main on a flight and none in Delta One or Delta Premium. American allows up to 5 pet carriers in the main cabin of American Eagle regional jets. Both airlines book pets on a first-come, first-served basis.
7. Get your pet used to the carrier weeks in advance. IATA advises letting pets become familiar with the crate “a few weeks or months before your planned departure.”
8. Leave time at check-in. Delta requires pet owners to check in at the Special Service Counter, and pets must be removed from the kennel at the security checkpoint.

What rules apply to the carrier at the airport and on board?

Seat restrictions. Delta, American and Southwest all bar pet carriers from exit rows, and Delta and American also bar them from bulkhead seats. Delta also excludes flat-bed seats and specific rows on its A330 aircraft.

Carry-on allowance. On Delta and American, the pet carrier counts toward your carry-on allowance. American Airlines states you can bring either a personal item or a carry-on bag with your pet carrier, not both.

Pets per carrier. Southwest allows up to two small cats or dogs of the same species in one carrier. Delta allows two pets in one kennel only if they are the same breed and size and between 8 weeks and 6 months old.

Sedation. IATA discourages sedating pets for air travel. American Airlines says it does not accept sedated or tranquilized pets, citing the American Veterinary Medical Association (AVMA) and the higher risk of respiratory and cardiovascular problems at altitude. Ask your veterinarian if you have concerns.

The carrier is only half the trip: travel documents

A compliant carrier gets your pet onto the plane. It does not get your pet across a border. Each set of documents comes from a different authority:

• United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) tells owners leaving the U.S. to contact a USDA-accredited veterinarian “as soon as you decide to travel” to meet destination requirements (APHIS pet travel page, updated March 20, 2026).
• U.S. Centers for Disease Control and Prevention (CDC) is the primary authority for dogs entering the United States. Delta's 2026 guidance notes that dogs entering the U.S. must be microchipped, at least 6 months old and accompanied by a completed CDC Dog Import Form receipt.
• New World Screwworm checks. Delta and American both report that from August 3, 2026, dogs entering Mexico need a New World Screwworm Inspection Certificate from a USDA-accredited veterinarian, issued no more than 5 days before arrival.
• European Union pet passport. The European Commission's Your Europe portal says the European pet passport is issued only to EU-resident owners of dogs, cats and ferrets. It records the microchip or tattoo code and rabies vaccination history, and it stays valid for life as long as vaccinations are in date.

Airline pet rules vs Animal Passport: not the same thing

Travel search results often mix up several different things called a “passport,” so here is how they differ:

• Airline pet policies (Delta, American, United, Southwest) set carrier size, fees and seating rules for pets in the cabin.
• The EU pet passport is an official EU identification document for dogs, cats and ferrets. Only an authorized veterinarian can issue one.
• Animal Passport is a digital animal and livestock identity record built on muzzle biometrics. The pattern on an animal's nose is unique, like a fingerprint. Owners capture it with a phone, and the record links the animal to its owner, breed, estimated age, body condition and vaccination history. Age is estimated from a dental photograph with a confidence score, and body condition is scored 1–5 from a side-profile photo.

Animal Passport is not an airline-approved travel document, an EU pet passport or a government-issued health certificate. It also does not replace a veterinarian's examination. Its main use so far is livestock identity: during flooding in Pakistan in August 2025, it helped farmers reclaim animals after paper tags washed away. If you are flying with a cat or dog, follow your airline's carrier rules and the official USDA APHIS, CDC or EU requirements above. You can read more about animal identification on the Animal Passport blog.

Bottom line

In September 2026, the safest choice is a soft-sided carrier around 18 x 11 x 11 inches, or 18 x 10.5 x 10 inches for Southwest, with ventilation on at least three sides and a leak-proof base. Before you buy, check that the carrier fits both your pet (using IATA's formula) and the smallest under-seat space on your itinerary. Then confirm the limit with your airline, because under-seat space varies by aircraft and airlines revise these limits over time.