Southwest Pet Carrier Dimensions: The Official Size Limits

Southwest pet carrier dimensions are capped at 18.5 inches long, 13.5 inches wide, and 9.5 inches high — the maximum size Southwest Airlines allows for an in-cabin pet carrier, according to the airline's official Optional Travel Charges page. The carrier, hard- or soft-sided, must fit entirely under the seat in front of you for the whole flight. This guide breaks down the exact limits, the current fee, and how Southwest's rule compares with other U.S. airlines.

Southwest's Official Pet Carrier Size Limit

Southwest Airlines' pet policy, published on its official support site, states that pet carriers must be small enough to stow under the seat and that pets — including head and tail — must stay inside the carrier for the entire time they're in the gate area, boarding, and in flight. Southwest's Optional Travel Charges page and multiple carrier-size references corroborate a maximum of 18.5 in (L) x 13.5 in (W) x 9.5 in (H) for third-party carriers used in the cabin.

Southwest also sells its own branded pet carrier through The Southwest Store. That carrier is smaller than the maximum allowed size, at approximately 17 in (L) x 10 in (W) x 9.5 in (H), and is pre-approved for Southwest flights since it was designed to fit under Southwest's own seats.

What Counts Toward the Dimensions

The measurement is of the carrier itself, not the space it takes up once compressed. A soft-sided carrier that expands or bulges when a pet moves inside it can still be rejected at the gate if a gate agent judges it won't fit flat under the seat. Southwest's policy notes carriers must be leak-proof and have a waterproof bottom with an absorbent pad, plus ventilation on at least three sides for domestic flights.

Soft-Sided vs. Hard-Sided Carriers on Southwest

Southwest accepts both soft-sided and hard-sided pet carriers, as long as either style stays within the 18.5 x 13.5 x 9.5-inch maximum. In practice, soft-sided carriers are the more forgiving choice: they compress slightly at the corners, which makes it easier to slide a carrier at the edge of the size limit under a narrower seat on regional aircraft like the Boeing 737-700. Hard-sided carriers hold their shape and protect the pet better from being squeezed, but they cannot flex if the under-seat space on your specific aircraft is tighter than expected. If you fly Southwest regularly with a pet close to the maximum dimensions, a soft-sided carrier reduces the risk of a gate agent asking you to check whether it fits.

Booking a Pet Reservation on Southwest

Southwest recommends booking your pet's spot in advance rather than showing up at the airport, because the airline caps the number of pet carriers allowed in the cabin on each flight. Pet fares are paid at the ticket counter, not online, and Southwest's policy states the fare is refundable if your travel plans change. Arrive early enough to complete the pet check-in process before the standard boarding cutoff, since agents need time to verify the carrier meets the airline's size and behavior requirements before you board.

Weight Limits: Southwest vs. Other Airlines

Southwest's published pet policy does not state a specific combined weight limit for the pet plus carrier — its restriction is based on carrier size and the animal's ability to stand up and turn around comfortably inside it. This differs from Delta Air Lines and United Airlines, both of which cap combined pet-and-carrier weight at 20 lbs in their official pet policies. If your dog or cat is on the larger side but still fits and can move comfortably in an 18.5 x 13.5 x 9.5-inch carrier, Southwest's rule is less restrictive on weight than Delta's or United's.

Southwest Pet Fees (Current)

As of Southwest's current Optional Travel Charges page, the in-cabin pet fee is $125 each way for U.S. mainland and Puerto Rico flights, and $35 each way for travel between the Hawaiian Islands. Southwest also sells its own branded pet carrier for $58 at the ticket counter. Southwest states this fee is subject to change at any time, so confirm the current rate on Southwest's Optional Travel Charges page before booking.

Southwest Pet Carrier vs. Delta vs. United

Southwest's carrier envelope is wider and taller than Delta's or United's soft-sided maximum, but all three require the carrier to fit fully under the seat, and actual clearance still depends on the specific aircraft's under-seat space.

How to Confirm Your Carrier Will Fit

1. Measure your carrier at its widest, tallest, and longest points, including feet, wheels, or zippered expansions.
2. Compare against Southwest's 18.5 x 13.5 x 9.5-inch maximum.
3. Make sure your pet can stand up, turn around, and lie down inside without the carrier bulging past its listed dimensions.
4. Call Southwest Reservations or check at the ticket counter if you're within an inch of the limit — gate agents make the final call.
5. Book your pet reservation in advance; Southwest limits the number of pet carriers allowed per flight.

Pet Carrier Size Rules Are Separate From Travel Paperwork

Southwest's carrier-size limit only governs what physically fits in the cabin. It has nothing to do with the paperwork needed to move a pet across state lines or borders. For interstate travel within the U.S., the United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) does not issue interstate pet certificates itself — individual state animal health offices set their own health-certificate and vaccination requirements, so check your destination state's rules separately from Southwest's carrier policy.

It's also worth being clear about what a "pet passport" is and isn't. The EU pet passport under the EU Pet Travel Scheme is an official government-issued document tied to a microchip and rabies vaccination record, used for cross-border travel within the EU. That is a different product from Animal Passport, which is a phone-based digital identity record that uses muzzle biometrics — a nose print unique to each animal, like a fingerprint — to bind an owner, breed, estimated age, body condition score, and vaccination history to an animal. Animal Passport's dental-photo age estimate and side-profile body condition score (1–5) are identity and welfare-record tools, not government travel documents, airline pet paperwork, or a substitute for a USDA health certificate. The tool has been used in livestock flood rescue in Pakistan in August 2025, helping farmers reclaim animals after paper ear tags were washed away — a very different use case from carrying a cat or dog through airport security. Read more on the Animal Passport blog.

Why Carrier Size Rules Exist

Under-seat pet carrier limits are not unique to Southwest — every U.S. airline that allows in-cabin pets sets a maximum size because the Federal Aviation Administration (FAA) requires all cabin baggage, including live animals in carriers, to be stowed in a way that does not block the aisle or emergency exit access. That safety requirement is why Southwest, Delta, and United all publish carrier dimensions rather than leaving it to passenger judgment, and why a carrier that is compliant on one airline is not automatically compliant on another. As of September 2026, Southwest's limit remains the widest of the three major carriers compared in this guide, but airlines can and do revise these numbers, so it's worth rechecking the airline's own page close to your travel date.

FAQ: Southwest Pet Carrier Dimensions

What is the maximum pet carrier size for Southwest Airlines?

Southwest allows in-cabin pet carriers up to 18.5 inches long, 13.5 inches wide, and 9.5 inches high, and the carrier must fit completely under the seat in front of you.

Does Southwest have a weight limit for pets?

Southwest's published pet policy does not list a specific combined weight limit for the pet and carrier; it instead requires the carrier to fit under the seat and allow the pet to stand up and turn around comfortably.

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

Southwest's current pet fee is $125 each way on U.S. mainland and Puerto Rico flights, and $35 each way between the Hawaiian Islands, according to Southwest's Optional Travel Charges page. Southwest notes this fare is subject to change.

Can I bring a large dog on Southwest in a carrier?

Only if the dog fits comfortably inside a carrier no larger than 18.5 x 13.5 x 9.5 inches and can stand up and turn around; Southwest does not transport pets in the cargo hold, so larger dogs cannot fly with Southwest at all.

Does Southwest sell its own approved pet carrier?

Yes. Southwest sells a branded pet carrier through The Southwest Store measuring roughly 17 x 10 x 9.5 inches, which is smaller than the airline's maximum allowed size.

How many pets can I bring in one carrier on Southwest?

Each pet carrier may hold up to two small cats or dogs of the same species, and each ticketed passenger is limited to one carrier.

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

No. A Southwest-compliant carrier only satisfies the airline's cabin-space rule; it has no bearing on government pet-travel documents like the EU pet passport or USDA APHIS export paperwork, and it is unrelated to identity tools like Animal Passport's muzzle-biometric record.

Do I need a health certificate to fly with my pet on Southwest?

Southwest's pet policy addresses carrier size and behavior rather than health paperwork; for interstate travel, contact your destination state's animal health office, since USDA APHIS does not set interstate pet-movement certificate requirements itself.