Southwest Airlines Pet Carrier Size: Official Dimensions, Fees & Rules

Southwest Airlines pet carrier size rules require the carrier to fit completely under the seat in front of you. Southwest’s own branded pet carrier measures 15 in (L) x 10 in (W) x 10 in (H), and any other carrier you bring must not exceed 18 in (L) x 10.5 in (W) x 10 in (H), according to Southwest Airlines’ official Help Center (checked September 2026). Southwest charges a $125 each-way pet fare on continental U.S. flights and does not publish a specific pound-based weight limit for pets.

Southwest Airlines Pet Carrier Size at a Glance

As of September 2026, Southwest Airlines’ Help Center lists two sets of dimensions depending on whether you use Southwest’s own carrier or an outside one:

These figures come directly from Southwest’s “What type of pet carriers can I bring?” article. It’s worth flagging that many independent pet-travel sites still quote a larger 18.5 x 13.5 x 9.5-inch limit and a 20-pound combined weight cap for Southwest. Those numbers do not appear anywhere on Southwest’s current official carrier or pet-policy pages as fetched for this article, and they more closely resemble figures used by other carriers or older policy versions. When in doubt, measure your carrier against the numbers above, not against a generic “airline-approved” label on a retail listing.

What Counts as an “Approved” Pet Carrier on Southwest?

Southwest Airlines’ Help Center specifies that a carrier must be:

• Specifically designed as a pet carrier — a tote bag or backpack that isn’t built for animal transport does not qualify.
• Leak-proof and well-ventilated, per Southwest’s official carrier guidance.
• Soft- or hard-sided — both are accepted, though Southwest recommends soft-sided carriers because under-seat space varies by seat type and aircraft.
• Roomy enough for the pet to stand up and turn around inside the carrier.
• Stowed under the seat in front of you for the entire time you’re in the gate area, boarding, deplaning, and in flight — it cannot occupy its own seat.

Southwest also restricts pet carriers from exit rows and bulkhead (front) rows, since there is no seat in front to stow the carrier under, according to Southwest’s onboard pet-travel guidance.

Does Southwest Have a Pet Weight Limit?

No. Southwest Airlines’ pet-policy pages, reviewed directly for this article, do not state a specific pound limit for a pet or a pet-plus-carrier combination. Instead, Southwest’s actual requirement is functional: the carrier has to fit under the seat, and the animal inside has to be able to stand up and turn around comfortably. In practice, that size ceiling — roughly the volume of an 18 x 10.5 x 10-inch box — does most of the work of limiting pet size, since most dogs and cats over about 15-20 pounds physically will not fit and stand upright in a carrier that small. If you see a specific weight number (commonly “20 lbs”) attached to Southwest online, treat it as a general guideline used across the pet-travel industry rather than a rule stated on Southwest’s own site.

Southwest Pet Travel Fees (2026)

Southwest Airlines charges a $125 pet fare each way for a pet carrier on flights within the continental United States, and $35 each way for flights between the Hawaiian Islands, according to Southwest’s Optional Travel Charges page (Southwest Airlines, 2026). The fare must be paid at the airport ticket counter and is charged per carrier, not per animal — so two cats sharing one carrier still pay a single pet fare.

This fee has climbed over time. Southwest raised its pet fare to $95 each way from $75, effective for flights on and after January 15, 2014, citing higher operating costs (Fox News, 2014). By September 2026, that fare had risen again to $125 each way, per Southwest’s own current fee page. Southwest notes on its site that “Pet Fare is subject to change at any time,” so travelers should check the live page before booking rather than relying on a cached figure from a blog post.

Booking and Eligibility Rules

Beyond size and cost, Southwest’s Help Center lays out several eligibility rules that determine whether a pet can fly at all:

1. Species: Only small domestic cats and dogs are accepted. Southwest does not carry other species in the cabin.
2. Minimum age: Pets must be at least eight (8) weeks old to travel, per Southwest’s official pet policy.
3. Cabin only: Southwest does not transport pets in the cargo hold under any circumstances — every pet flies in the cabin, in an approved carrier, at the passenger’s feet.
4. One carrier per customer: Each ticketed customer may bring one pet carrier, and each carrier may hold up to two small cats or dogs of the same species if there’s enough room for both.
5. No international travel: Southwest states plainly that pets are not allowed on international flights or on any itinerary that includes an international segment.
6. Vaccination: Pets must be vaccinated, consistent with Southwest’s general pet-eligibility requirements.
7. Reserve early: Southwest’s Help Center recommends booking your pet’s spot in advance by phone, noting that “space is limited” for in-cabin pets on each flight.

Southwest also warns that pets showing disruptive behavior — excessive noise, growling, biting, jumping, lunging, or eliminating in the cabin or gate area — may be denied boarding, and that animals with heart disease, anxiety disorders, or brachycephalic (flat-faced) airways face a higher risk of complications during flight, per Southwest’s own pet-policy guidance.

Southwest vs. Delta: How Carrier Rules Compare

Carrier-size rules are airline-specific, not industry-wide, so a carrier that fits on one airline may not fit on another. Delta Air Lines, for comparison, recommends a soft-sided kennel no larger than 18 x 11 x 11 inches and charges $150 each way for tickets issued on or after April 8, 2025, up from $95 for tickets issued before that date (Delta Air Lines, 2026). Delta also notes that under-seat space varies by aircraft type, so its 18 x 11 x 11-inch figure is a recommendation for fitting “most” aircraft rather than a guarantee on every flight.

The takeaway: never assume a carrier “approved” for one airline automatically clears another airline’s under-seat space. Always re-check the specific airline’s live policy page for your booking.

How to Fly with a Pet on Southwest: Step by Step

1. Confirm eligibility. Make sure your pet is a cat or dog, at least 8 weeks old, and vaccinated.
2. Pick a compliant carrier. Measure it against Southwest’s 18 x 10.5 x 10-inch external limit (or use Southwest’s own 15 x 10 x 10-inch carrier), and confirm it’s leak-proof and well-ventilated.
3. Book early. Reserve your pet’s spot ahead of time, since Southwest limits how many in-cabin pets it accepts per flight.
4. Pay the pet fare at the airport. Southwest collects the $125 (or $35 for Hawaii inter-island) fare at the ticket counter, not online.
5. Go through security together. You’ll carry your pet through the screening device by hand while the empty carrier is X-rayed, per Southwest’s airport guidance.
6. Keep your pet in the carrier the whole time — in the gate area, during boarding and deplaning, and for the entire flight, stowed under the seat in front of you.

A Note on Pet Identification Before You Fly

Southwest’s pet fare and carrier-size rules govern how your pet travels, not how it’s identified if a collar or tag comes loose. Standard travel advice — a secure collar with an ID tag and an up-to-date microchip registration — still applies for any cat or dog flying in-cabin. That kind of identification is separate from, and not required by, Southwest’s pet policy.

It’s also worth being precise about terminology, since “pet passport” gets used loosely online. A Southwest pet carrier has nothing to do with the EU’s official pet travel scheme or any government-issued travel document — and it’s a different tool entirely from Animal Passport, which is a digital livestock-identification product, not an airline or government document. Animal Passport uses phone-based muzzle biometrics — a nose print, which is unique the way a human fingerprint is — along with a dental-photo age estimate and a body-condition score, to help owners prove ownership of livestock such as cattle. It was used during livestock flood rescue efforts in Pakistan in August 2025, helping farmers reclaim animals after paper ear tags had washed away. It is not marketed as a cat or dog travel carrier, an airline document, or a substitute for a government pet passport. Readers interested in how biometric animal identification is being used in the field can see more examples on the Animal Passport blog.

Southwest Airlines: “Pet Fare is subject to change at any time.” Always confirm current dimensions and fees on Southwest’s live Help Center before you book, rather than relying on a cached figure from a third-party site.