Southwest Pet Carrier Size: Official Dimensions, Fees, and Rules for 2026

The Southwest pet carrier size limit is 18.5 inches long by 13.5 inches wide by 8.5 inches high — small enough for a soft- or hard-sided carrier to fit fully under the seat in front of you. Southwest Airlines allows one carrier per ticketed passenger, charges a $125 one-way pet fare in the mainland U.S., and limits most flights to six pet carriers total. This guide breaks down the official dimensions, fees, and booking rules as of August 2026.

What Is the Maximum Southwest Pet Carrier Size?

According to Southwest Airlines' official pet policy, an in-cabin pet carrier cannot exceed 18.5 inches long x 13.5 inches wide x 8.5 inches high. That 8.5-inch height limit is stricter than many popular carrier brands advertise as "airline approved," so it is worth measuring your carrier — loaded with the pet inside, since soft sides bulge — before you get to the airport.

Southwest's carrier rules also require that the carrier be:

• Soft-sided or hard-sided, as long as it stays within the size limit
• Leak-proof on the bottom
• Well ventilated on multiple sides
• Small enough to stow completely under the seat in front of the passenger

Southwest counts the pet carrier as the passenger's one carry-on bag or personal item, so you cannot bring a separate roller bag and a full-size carry-on in addition to the pet carrier.

Why the 8.5-Inch Height Limit Trips People Up

Many carriers marketed online as "airline approved" are built to an 11-inch height, which fits some airlines' general pet-carrier guidance but exceeds Southwest's 8.5-inch ceiling. Southwest's limit is tied to actual under-seat clearance, which varies by aircraft type and even by row, since bulkhead rows, exit rows, and rows near in-flight entertainment boxes can have less foot space than standard rows. A carrier that measures 8.5 inches empty may also expand once a pet settles inside, especially soft-sided designs with mesh panels that bow outward. For that reason, measure the carrier loaded with your pet inside, not just the manufacturer's spec sheet, and confirm your specific carrier with a Southwest agent before travel day if you are unsure it will clear the seat in front of you.

Choosing a Carrier That Fits Southwest's Size Limit

Because the 8.5-inch height cap is stricter than many other domestic carriers' pet rules, it helps to shop with Southwest's exact numbers in hand rather than relying on generic "airline approved" labeling, which is a marketing term and not a Southwest certification. When evaluating a carrier for a Southwest flight, look for:

• Overall dimensions at or below 18.5" L x 13.5" W x 8.5" H once your pet is inside and the sides settle
• Soft, collapsible sides rather than rigid plastic shells, which compress more easily under a seat
• Mesh ventilation panels on at least two sides for airflow during the flight
• A leak-proof, wipeable base lined with an absorbent pad
• Low-profile zippers and no protruding wheels, handles, or hardware that could catch on the seat frame

If a carrier's manufacturer lists dimensions close to Southwest's limit, contact Southwest directly rather than assuming a third-party retailer's "fits Southwest" claim is accurate, since Southwest's gate and ticket-counter staff make the final call on whether a carrier is accepted.

Southwest Pet Carrier Size at a Glance

Source: Southwest Airlines' official Pet Policy and Optional Travel Charges pages, verified August 2026.

How Many Pets Can Fit in One Carrier?

Southwest allows up to two small cats or dogs of the same species inside a single compliant carrier, provided both animals can stand, turn around, and lie down comfortably within the 18.5 x 13.5 x 8.5-inch limit. Mixing a cat and a dog in the same carrier, or exceeding the size limit to fit two larger pets, is not permitted.

Southwest Pet Travel Fees (2026)

Southwest Airlines charges a $125 one-way pet fare for travel within the mainland United States, and a reduced $35 one-way fare for pets traveling between the Hawaiian Islands, according to Southwest's Optional Travel Charges page. The fee applies per pet carrier, not per animal, so two same-species pets sharing one compliant carrier still pay a single fare. Southwest does not permit pets to travel to or from Hawaii on flights connecting to the mainland — only inter-island Hawaii routes accept pets.

The pet fare must be paid at the Southwest ticket counter and is refundable if the reservation is canceled.

Booking Rules and Carrier Limits Per Flight

Southwest limits most flights to around six pet carriers in the cabin, accepted on a first-come, first-served basis, though the airline notes this number can vary by aircraft and route. Because space is limited and not guaranteed at check-in, Southwest recommends calling reservations in advance to add your pet to the flight before arriving at the airport.

1. Confirm your carrier measures no more than 18.5" x 13.5" x 8.5" with the pet inside.
2. Call Southwest reservations ahead of your flight to reserve one of the limited pet-carrier spots.
3. Pay the pet fare ($125 mainland, $35 inter-island Hawaii) at the ticket counter.
4. Keep the pet inside the carrier at all times in the gate area, during boarding, deplaning, and the flight.
5. Walk the carrier through the X-ray screening machine at TSA security with your pet inside.

Southwest Pets vs. Service Animals: What Changed

Southwest's paid pet program is separate from its service-animal policy. Effective March 1, 2021, Southwest Airlines stopped accepting emotional support animals and now transports only trained service dogs that perform work or tasks for a passenger with a disability, a change Southwest attributed to a U.S. Department of Transportation rule change, per Southwest's investor relations announcement. Emotional support animals now fly under Southwest's standard paid pet policy — meaning they are subject to the same 18.5 x 13.5 x 8.5-inch carrier size limit, carrier count restrictions, and pet fares described above, not a separate service-animal process.

Southwest's Carrier Size Rule vs. Government Pet Travel Documents

Southwest's carrier dimensions are an airline carry-on rule, not a government-issued travel document. They should not be confused with official identity or health paperwork such as a European Union pet passport under the EU's pet travel scheme, or a USDA-endorsed international health certificate — both of which govern cross-border pet movement, not cabin bag sizing. The International Air Transport Association (IATA) separately publishes Live Animals Regulations that set global welfare and container standards airlines reference when building their own pet policies, including Southwest's. The current IATA Live Animals Regulations edition, effective January 1, 2026, sets standards for container construction, ventilation, and handling that inform how commercial airlines worldwide, including U.S. carriers, think about pet and animal containers — even though Southwest's specific 18.5 x 13.5 x 8.5-inch cabin limit is its own operational rule rather than an IATA mandate.

International travelers should also note that flying with a pet often involves paperwork Southwest's domestic pet policy does not cover, such as USDA-endorsed health certificates for interstate or international movement, or destination-country entry requirements. Southwest's pet policy governs only the carrier size, fee, and in-cabin conduct for its own flights; it does not replace health certificates, state entry rules, or the documentation required by a destination country or connecting international carrier.

It's also worth distinguishing Southwest's rules from products like Animal Passport, a digital identity record for livestock that uses a phone-captured muzzle print — a nose print pattern that is unique to each animal, similar to a human fingerprint — to bind an owner, breed, estimated age, body condition score, and vaccination history to one record. Animal Passport is built for farm and field use, including reuniting flood-displaced livestock with owners in Pakistan in August 2025 after paper ear tags washed away, and it is not an airline travel document, a veterinary diagnostic tool, or a substitute for a government pet passport. If you're researching identity tools for farm animals rather than cabin pet carriers, the Animal Passport blog covers how biometric livestock ID differs from paper tagging and official travel paperwork.

Frequently Asked Questions

What is the maximum pet carrier size for Southwest Airlines?

The maximum Southwest pet carrier size is 18.5 inches long, 13.5 inches wide, and 8.5 inches high, and the carrier must fit fully under the seat in front of the passenger.

How much does it cost to fly with a pet on Southwest?

Southwest charges $125 one-way per pet carrier for travel within the mainland United States, and $35 one-way per carrier for flights between the Hawaiian Islands.

Can I bring two pets in one carrier on Southwest?

Yes. Southwest allows up to two cats or dogs of the same species in a single carrier as long as both animals fit comfortably and the carrier stays within the 18.5 x 13.5 x 8.5-inch limit.

Does Southwest allow pets in the cargo hold?

No. Southwest Airlines only transports pets in the cabin under the seat; it does not offer cargo-hold pet transport.

Can I fly with a pet to Hawaii on Southwest?

No. Southwest does not carry pets on flights to or from Hawaii from the mainland; pets are only permitted on flights between the Hawaiian Islands.

Do I need to book my pet's seat in advance on Southwest?

Yes, it's recommended. Southwest typically limits flights to about six pet carriers on a first-come, first-served basis, so calling reservations ahead of time helps secure a spot.

Are emotional support animals still allowed on Southwest?

No. Since March 1, 2021, Southwest only accepts trained service dogs as service animals; emotional support animals must travel under the standard paid pet policy and its carrier-size rules.

Is a Southwest-approved pet carrier the same as a pet passport?

No. A Southwest-approved carrier is an airline carry-on sizing rule, while a pet passport (such as under the EU pet travel scheme) is a government travel document, and a biometric livestock ID like Animal Passport is a separate identity record for farm animals — the three serve different purposes and should not be confused.