Flying Southwest With Your Dog: Cabin Only, $125 and No Hold
Southwest keeps it simple: a small dog under the seat, domestic flights only, and no cargo hold at all. If your dog doesn't fit in a bag, Southwest is not your airline. Here's the short version, checked September 2026. Confirm on Southwest's own pet policy before you book.
In the cabin: bag size, not weight
Southwest publishes no weight limit for dog and carrier together. The bag size is what counts.
- Your own carrier: max 18 × 10.5 × 10 in (45.7 × 26.7 × 25.4 cm).
- Southwest's own carrier: 15 × 10 × 10 in (38.1 × 25.4 × 25.4 cm), sold at the airport.
- How many: one carrier per passenger, with up to two cats or two dogs of the same species inside it.
- Age: at least 8 weeks old.
The bag goes under the seat in front of you, and a soft-sided one is easier because an aisle seat has less room. Your dog stays in it the whole time, including at the gate and while boarding. Head and tail inside, and it should be able to stand up and move around.
What it costs
- US mainland: $125 per carrier, one way.
- Between the Hawaiian islands: $35 one way.
You pay at the ticket counter, and unlike most airlines Southwest refunds the fee if you cancel the reservation.
Where your dog can't come
No pets on international flights, or on any itinerary that contains one. No pets between the mainland and Hawaii either, although flights between the Hawaiian islands are fine. Travelling to Puerto Rico means extra USDA paperwork. Children flying as unaccompanied minors can't take a pet at all.
No hold, no cargo
Southwest states plainly that no pets are carried in the cargo compartment. There is no checked-baggage option and no cargo service, so a bigger dog has to fly with a different airline. Our comparison of 27 airlines shows which ones do take dogs in the hold.
Breed rules
Southwest publishes no breed restrictions: only vaccinated domestic cats and dogs, no other species. Because there is no hold, the snub-nosed bans other airlines apply simply don't come up.
What you can still bring on board
Good news compared with most US airlines: the carrier counts as either your carry-on or your personal item, so you can still bring one other bag alongside it. On board you can't take the first row or an exit row, and your dog may never sit on a seat.
Does your dog fit?
Our free Dog Flight Checker takes your dog's weight and tells you whether Southwest, and 26 other airlines, take it in the cabin or the hold. It works out the bag length your dog needs to lie down.
Also flying with: American Airlines · Delta. Need a bag? Which Dog Carrier Bag Is Really Airline-Approved?
Source: Southwest Airlines pet policy, carrier and fee pages, checked September 2026. Always confirm with the airline before you book.