Southwest Airlines Pet Carrier Dimensions: Size Limits, Fees, and Fit Rules

As of September 2026, Southwest Airlines pet carrier dimensions for most third-party carriers are a maximum of 18 inches long by 10.5 inches wide by 10 inches high, according to the Southwest Airlines Help Center article on approved pet carriers. Southwest Airlines’ own branded carrier is listed at 15 inches long by 10 inches wide by 10 inches high. The carrier must fit under the seat in front of you, be leak-proof and well ventilated, and allow your small vaccinated cat or dog to stand and move around with ease.

Southwest Airlines pet carrier dimensions are the airline’s published exterior size limits for in-cabin pet kennels on domestic flights—cabin-only travel with no cargo pet option under Southwest Airlines’ Contract of Carriage.

This guide from Animal Passport answers the size question first, then covers fees, booking, airport steps, and how airline pet rules differ from digital livestock identity tools. Rules change; always recheck Southwest.com before you fly.

Official Southwest Airlines pet carrier dimensions

Southwest Airlines’ Help Center page “What type of pet carriers can I bring?” states that acceptable carriers must be specifically designed as pet carriers, leak-proof, well ventilated, and within these published dimensions:

• Southwest Airlines Pet Carrier: 15" (L) × 10" (W) × 10" (H)
• Other pet carriers (maximum): 18" (L) × 10.5" (W) × 10" (H)

The same Help Center article recommends a soft-sided carrier because under-seat space varies by seat type and location, and notes that aisle seats may offer more limited space for pet carriers. Your pet—including head and tail—must remain completely inside the carrier and be able to stand up and move around the carrier with ease.

Southwest Airlines’ Contract of Carriage (Passenger) does not print a separate inch chart in the pets section. Instead, Section 4.e requires an appropriate pet carrier that is leak-proof and well ventilated, small enough to fit under the seat in front of the passenger, and stowed there for the entire flight. Passengers traveling with a pet may not occupy an exit row seat or a seat with no forward under-seat stowage, per that Contract of Carriage.

Why some sites still list 18.5 × 13.5 × 8.5 inches

As of September 2026, several consumer travel sites still quote older Southwest Airlines pet carrier dimensions of about 18.5 inches long by 13.5 inches wide by 8.5 inches high. Those figures do not match the dimensions currently published on Southwest Airlines’ approved pet carriers Help Center article (18" × 10.5" × 10" for other carriers). Sources disagree. Treat the Help Center and Contract of Carriage on Southwest.com as controlling, measure your carrier’s exterior including handles and mesh bulge, and confirm under-seat fit on your aircraft type if you can.

Who and what can fly in a Southwest pet carrier

Under Southwest Airlines’ pet policy and Contract of Carriage, Southwest may accept small vaccinated domestic cats and dogs that are at least eight (8) weeks old, contained in a pet carrier, and traveling with a passenger. Key limits include:

• One pet carrier per ticketed customer / passenger
• Up to two animals of the same species per carrier
• Unaccompanied Minors may not travel with a pet
• Southwest reserves the right to limit pet carriers to six (6) per flight, accepted first-come, first-served
• No pets in the cargo compartment
• No pets on international itineraries (Contract of Carriage Section 8)

Southwest Airlines’ Optional Travel Charges page states that Southwest accepts small vaccinated domestic cats and dogs as in-cabin pets in an appropriate carrier, and that each pet carrier counts as a carryon or personal item. There is no separate published pet weight limit on the Help Center carrier article; fit and comfort inside a compliant under-seat carrier are the practical constraints.

Pet fare and what counts as your bag

As of the fees published on Southwest Airlines’ Optional Travel Charges page, the one-way carry-on pet charge is $125 per pet carrier on U.S. Mainland itineraries and $35 per pet carrier between Hawaiian Islands. Southwest notes that Pet Fare pricing is subject to change at any time. The Help Center pet policy states the Pet Fare must be paid at the Southwest ticket counter with accepted credit cards and is refundable if you cancel the reservation.

The same Optional Travel Charges table lists a Southwest merchandise pet carrier at $58 per carrier for purchase at the ticket counter. Pet carriers are treated as either a personal item or a carry-on item: you may board with a pet carrier plus a personal item, or a pet carrier plus a regular-size carry-on bag, according to Southwest’s airport expectations article for pets.

How to book and what happens at the airport

1. Reserve by phone. Southwest Airlines’ Contract of Carriage states pet reservations can only be booked by calling Southwest; space is limited.
2. Arrive with pets already in an approved carrier. Proceed to the airport ticket counter to check the pet(s) in and pay the Pet Fare before going to the departure gate.
3. Security screening. Southwest’s airport expectations article says you hold your pet and walk through the screening device while the carrier is X-rayed; all pet carriers are subject to search.
4. Gate and onboard. Pets (including head and tail) must stay secured in the carrier in the gate area, during boarding and deplaning, and for the entire flight. Carriers must be stowed under the seat in front of you. Pets must never occupy a passenger seat and may not be located in an exit row or the first row (bulkhead), per Southwest’s onboard expectations article.
5. Behavior rules. Disruptive behavior—such as excessive barking, growling, biting, or eliminating in the cabin or gate area—may result in denied boarding, according to Southwest’s pet policy materials.

Pet relief areas are available at locations Southwest serves, but Southwest states it will not hold a flight for a relief break. Standard checked bag fees apply if you check a pet stroller; Southwest does not assume liability for damage to pet strollers.

Airline cabin rules vs. USDA APHIS commercial transport rules

It is easy to mix airline under-seat policies with federal commercial shipping standards. The United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) states that transportation of pets that remain in the custody of their owners—for example, pets that travel in the cabin of an aircraft with their owner—is not regulated under the Animal Welfare Act (AWA). APHIS does regulate businesses that take custody of covered animals and transport them for hire, such as cargo shipments.

Separately, USDA APHIS “Pets on Planes” training describes kennel suitability, health readiness, and documentation practices commonly associated with preparing dogs and cats for air transport. That lesson notes USDA regulations requiring dogs and cats to be at least 8 weeks old and fully weaned before traveling—language that aligns with Southwest’s eight-week minimum—but hard-sided cargo kennel labeling and “Live Animal” marking requirements are aimed at commercial/cargo-style shipments, not Southwest’s in-cabin soft carrier model. For owner-accompanied cabin travel on Southwest, follow Southwest’s published carrier dimensions and Contract of Carriage first.

For interstate trips, USDA APHIS states that APHIS does not regulate the interstate movement of pets by their owners; destination state or territory animal health requirements (health certificates, vaccinations, tests, or treatments) are set by the receiving jurisdiction. Contact your veterinarian early and check APHIS Pet Travel state pages for your destination.

How this differs from Animal Passport’s biometric livestock ID

Airline pet carrier rules and EU-style pet travel documents are not the same product as Animal Passport. Animal Passport is a digital animal and livestock passport that uses muzzle biometrics—a nose print unique like a fingerprint—captured by phone. The record can bind owner, breed, estimated age, body condition, and vaccination history. Age can be estimated from a dental photograph with a confidence score, and body condition can be scored 1–5 from a side-profile photo.

In August 2025 livestock flood rescue work in Pakistan, biometric identity helped farmers reclaim animals when paper tags washed away—an ownership and recovery use case, not a Southwest boarding pass. Animal Passport is not a government-issued airline travel document, does not replace Southwest’s Pet Fare or carrier size rules, and does not provide veterinary diagnosis or legal advice. For more field notes on identity versus travel paperwork, see the Animal Passport blog.

Practical measuring checklist before you buy or pack

• Measure the carrier’s full exterior length, width, and height, including mesh panels, zippers, and side pockets.
• Compare those numbers to Southwest’s published maximum of 18" × 10.5" × 10" for non-branded carriers (or 15" × 10" × 10" for the Southwest-branded model).
• Confirm your pet can stand, turn, and lie down comfortably with the door closed—Southwest requires ease of movement inside the carrier.
• Prefer soft-sided construction if you need a little compressibility under different seat geometries, as Southwest recommends.
• Practice airport routines: pet out for security walk-through, carrier through X-ray, then back inside before the gate area.
• Book early by phone; six carriers per flight is the Contract of Carriage cap Southwest reserves the right to apply.

Experience note from Animal Passport’s livestock identity work: paper tags and single physical markers fail first in floods and chaotic moves. For cabin pets, the parallel lesson is redundancy—confirm carrier size against the current airline page, keep vaccination records accessible, and do not assume an older blog measurement still matches Southwest’s Help Center.

As of September 2026, the safest path is simple: use Southwest Airlines’ current Help Center dimensions, pay the published Pet Fare at the ticket counter, keep the animal fully inside a leak-proof ventilated carrier under the seat, and verify any state entry health rules with USDA APHIS and your veterinarian. That combination answers the search for Southwest Airlines pet carrier dimensions and keeps boarding day predictable.