Pet Carrier Dimensions for Southwest Airlines: Official Size Limits

Southwest Airlines' current published pet carrier dimensions are 18" (L) x 10.5" (W) x 10" (H) for a standard soft- or hard-sided carrier, or 15" x 10" x 10" for Southwest's own branded carrier, according to Southwest Airlines' pet carrier guidelines page (Southwest Airlines, 2026). The carrier must fit completely under the seat in front of you, and your cat or dog must be able to stand up, turn around, and move inside it with ease. Southwest charges $125 each way for pets in the cabin on U.S. mainland flights (Southwest Airlines, 2026).

Those numbers matter because a lot of pages ranking for this topic repeat a different set of figures — often 18.5" x 13.5" x 9.5" with a 20-lb combined weight cap. Those figures do not appear on Southwest's currently published policy pages as of September 2026. Below is what Southwest's own pages say today, why the discrepancy likely exists, and how to measure your carrier so you're not turned away at the gate.

Southwest Airlines Pet Carrier Dimensions: The Official Numbers

Southwest publishes two sets of maximum carrier dimensions on its help center: one for the airline's own branded pet carrier, and one ceiling for any other carrier a customer brings.

Southwest requires that carriers be "specifically designed as pet carriers," leak-proof, and well ventilated, and that the animal — including head and tail — fit completely inside with room to stand up and move around (Southwest Airlines, 2026). Southwest recommends a soft-sided carrier because under-seat space differs by seat type and where you're seated on the plane; a hard-sided carrier is allowed only if it still fits within the dimensions above at your specific seat.

Is There a Pet Weight Limit on Southwest Airlines?

As of September 2026, Southwest's official pet carrier page does not list a pound-based weight limit for the pet or the pet-plus-carrier combination. Instead, the airline's stated standard is functional: the cat or dog must be able to stand up and move around inside the carrier with ease, and the loaded carrier must fit under the seat in front of you. In practice, that under-seat space is the real constraint — a stocky 18-lb cat may fit comfortably while a long-limbed 12-lb dog may not, depending on the carrier's shape.

If you've seen a "20 lb combined weight limit" cited elsewhere, treat it as a common but currently unsourced claim rather than Southwest's published rule. Call Southwest directly at the number on your reservation or check the airline's help center immediately before booking, since carrier and cabin policies can change without a public revision date.

Official Southwest Numbers vs. Commonly Repeated Numbers

Because several third-party pet-travel blogs cite different dimensions and fees than Southwest's own site, here's a side-by-side comparison to clear up the confusion.

When primary and secondary sources disagree this much, the safest move is to confirm current limits directly with Southwest before you book, rather than relying on any single blog post — including this one, months or years after publication.

What Southwest's Official Pet Policy Requires Beyond Size

• Age: Pets must be at least eight weeks old to travel (Southwest Airlines, 2026).
• Species and vaccination: Southwest accepts small, vaccinated domestic cats and dogs in the cabin on domestic flights only.
• Fee: $125 each way per pet carrier for U.S. mainland flights; $35 each way for interisland Hawaii flights (Southwest Airlines, 2026).
• Carrier allowance: One pet carrier per ticketed customer, counted as your carryon bag or personal item — you may not bring the carrier plus both a separate carryon and a personal item.
• Multiple pets: Up to two small cats or dogs of the same species may share one carrier if there's adequate room.
• Health risk factors: Southwest notes that animals with heart disease, anxiety disorders, or brachycephalic (short-nosed) airways are more susceptible to complications during flight.
• Behavior: Pets showing disruptive behavior — scratching, excessive barking, growling, biting, lunging, or eliminating in the cabin — may be denied boarding.
• Rapid Rewards: Pets do not earn Rapid Rewards points.

Southwest does not offer a cargo-hold pet option; all pets travel in the cabin, under the seat, for the entire flight.

How to Measure Your Pet Carrier Correctly

1. Measure the carrier's exterior length, width, and height at its widest points, including any wheels, pockets, or expandable mesh panels that stick out — gate agents measure the carrier as it will actually sit under the seat, not its folded or collapsed size.
2. Compare those numbers against 18" x 10.5" x 10" (or 15" x 10" x 10" if it's Southwest's own branded carrier).
3. Put your pet inside and confirm it can stand up, turn around, and lie down without its head, tail, or paws pressing against the mesh.
4. If you're unsure your carrier will fit under a specific aircraft's seat, choose a soft-sided model — Southwest specifically recommends soft-sided carriers because they compress slightly to fit varying under-seat dimensions, while hard-sided carriers cannot.
5. Call Southwest reservations before you fly to confirm your pet's spot, since in-cabin pet space is limited and handled separately from standard seat assignments.

Do You Need a Pet Passport for a Southwest Flight?

No — a domestic Southwest Airlines flight within the United States does not require a pet passport. "Pet passport" most often refers to the European Union's harmonized pet travel document used for moving cats, dogs, and ferrets between EU member states and the UK, which is issued by an official veterinarian and is a legal travel document under EU animal health rules. It is unrelated to Southwest's cabin pet policy.

For pet travel between the United States and other countries, the United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) — not the airline — sets export and import requirements, which can include a USDA-endorsed health certificate depending on the destination country (USDA APHIS, 2026). APHIS's own guidance addresses moving pets between the U.S. and other countries; the agency separately addresses interstate travel within the U.S. Because these federal rules are country-specific and can change, check the APHIS pet travel pages directly, or your veterinarian, before any international trip.

It's worth being clear about a second, unrelated meaning of "pet passport" that has emerged more recently: Animal Passport (https://www.animalpassport.co/) is a digital identity record that uses a phone-captured muzzle photo — an animal's nose print, which is unique like a human fingerprint — to bind an owner to a specific animal, along with breed, an estimated age from a dental photo, a body condition score from a side-profile photo, and vaccination history. It was used during livestock flood rescue efforts in Pakistan in August 2025, helping farmers reclaim animals after paper ear tags were washed away. This is a biometric identity and record-keeping tool, not a government-issued travel document, and it does not replace an EU pet passport, a USDA APHIS health certificate, or any airline's boarding requirements. If you want a simple way to keep your own pet's vaccination history organized before a trip, it's a useful personal record — just don't expect it to satisfy Southwest's gate requirements or a country's import rules. More travel-and-pet-ID context is on the Animal Passport blog at https://www.animalpassport.co/blogs.

Quick-Reference Checklist Before You Fly Southwest With a Pet

• Carrier measures at or under 18" x 10.5" x 10" (or 15" x 10" x 10" for Southwest's branded carrier).
• Pet can stand up, turn around, and lie down inside the closed carrier.
• Pet is at least eight weeks old and vaccinated.
• You've budgeted $125 each way (mainland) or $35 each way (interisland Hawaii) for the pet fee.
• You've called Southwest in advance to confirm your pet has a reserved spot in the cabin.
• You're flying domestically — Southwest does not carry pets in the cabin on international itineraries, and Hawaii-mainland pet travel is restricted.

Frequently Asked Questions

What size carrier does Southwest Airlines allow in the cabin?

Southwest's maximum published size for a non-branded pet carrier is 18 inches long, 10.5 inches wide, and 10 inches high; its own branded carrier is 15" x 10" x 10" (Southwest Airlines, 2026).

Does Southwest have a weight limit for pets?

Southwest's current official pet carrier page does not publish a specific weight limit. Instead, the pet must fit completely inside the carrier and be able to stand up and move around with ease.

How much does it cost to bring a pet on Southwest Airlines?

The in-cabin pet fee is $125 each way for U.S. mainland flights and $35 each way for interisland Hawaii flights, according to Southwest's Optional Travel Charges page (Southwest Airlines, 2026).

Can I bring my pet with me to or from Hawaii on Southwest?

Southwest offers a discounted $35 pet fee for interisland Hawaii flights, but destination-specific restrictions can apply to Hawaii pet travel; confirm current rules for your exact route with Southwest before booking.

How many pet carriers does Southwest allow per flight?

Southwest's help center confirms one pet carrier per ticketed customer, but does not publicly state a fixed total number of pet carriers per flight; some third-party sites cite a six-carrier cap, which travelers should verify by phone since cabin pet space is limited and reserved in advance.

Can two cats or two dogs share one carrier on Southwest?

Yes. Southwest allows up to two small cats or dogs of the same species to travel in a single carrier if there is adequate room for both animals to stand, turn around, and lie down.

Do I need a pet passport to fly my dog or cat on Southwest?

No. A domestic Southwest flight within the United States does not require a pet passport; that term usually refers to the European Union's official pet travel document, which has no bearing on Southwest's U.S. cabin pet policy.

Are certain dog or cat breeds restricted from flying on Southwest?

Southwest does not publish a breed ban, but it does warn that animals with heart disease, anxiety disorders, or brachycephalic (short-nosed) airways face a higher risk of complications during flight, so owners of those pets should talk to a veterinarian before booking.