Southwest Personal Item Size: Ensuring Your Bag Fits Under the Seat

According to Southwest’s carry-on and personal item policy, a personal item is a bag that goes under the seat in front of you [1].

Southwest does not publish maximum dimensions for a personal item [1]. It used to: until mid-2023 its page gave 18.5 x 13.5 x 8.5 inches, then 16.25 x 13.5 x 8 inches, which it described as the smallest space under its seats [3], and in November 2024 it removed the numbers again [4]. Both older figures still circulate online.

The one under-seat size Southwest does publish is for pet carriers, which must fit under the seat in front of you: up to 18 x 10.5 x 10 inches, or 15 x 10 x 10 inches for Southwest’s own carrier [5]. A bag within those dimensions is a reasonable target for a personal item, although Southwest does not promise that it will fit.

Southwest’s own examples of personal items include [1]:

• Backpacks

• Purses, including cross-body bags

• Laptop cases and briefcases

• Small cameras

• A pillow or blanket (neck pillows do not count toward the limit)

While Southwest does not publish a weight limit for these items, it decides whether any bag can travel in the cabin because of its weight, size, contents or character, and every carry-on item must be stowed under a seat or in an overhead bin [6].

On Southwest, every passenger may bring one carry-on bag of up to 24 x 16 x 10 inches, which goes in the overhead bin, and one personal item, which goes under the seat in front of you [1]. Southwest moved from open seating to assigned seats on January 27, 2026, and now boards passengers in Groups 1 to 8 [7]. Your group depends on your fare, Rapid Rewards tier, credit card and seat, and Basic fares board last, in Group 8 [8]. Space onboard is limited, and carry-on bags sometimes have to be checked at the gate [9].

Ensuring your “personal item” actually fits under the seat is a strategic move. A gate-checked carry-on comes back at baggage claim at your final destination, and before it goes you must remove any e-cigarettes, power banks, smart-bag batteries, spare batteries, lighters and matches; Southwest also recommends taking out medication, assistive devices such as canes, and keys [9]. A personal item that fits keeps those essentials at your feet. It is also where your power bank belongs: since April 20, 2026, each passenger may carry one power bank of up to 100 watt-hours, which must not go in the overhead bin and should be stored in a personal item under the seat [10].

Southwest itself says that under-seat space is not the same everywhere: it recommends soft-sided pet carriers because the space under the seat varies with seat type and location on the aircraft, and it can be more limited in some seats, including aisle seats [5]. When it still published a personal-item size in 2023, it described 16.25 x 13.5 x 8 inches as the smallest length, width and height available under its seats, adding that measurements vary by seat type and aircraft [3].

Travelers report the same: the travel blog Your Mileage May Vary noted in 2024 that under-seat space differs a lot between window, middle and aisle seats on Southwest [4].

• Aisle Seats: Southwest warns that space for pet carriers may be more limited here [5].

• Middle and Window Seats: Southwest gives no figures. With assigned seating you choose your seat at booking on most fares, while Basic fares get a seat at check-in [7].

• Boeing 737-800 vs. 737 MAX 8: Southwest does not publish under-seat sizes by aircraft type, so treat claims that one model has more room with caution.

To keep the whole trip cheap, use our 10 pro tips for finding the cheapest flights, then pack so everything fits in the free carry-on and personal item: checked bags now cost $45 and up on most fares [2].

A few items are handled outside your “one bag plus one personal item” limit:

• Outerwear: Coats and wraps you carry in the cabin are not considered baggage [6].

• Assistive Devices: Mobility and other assistive devices used by a passenger with a disability may be carried in addition to the carry-on allowance; one that cannot go in the cabin is checked free of charge [6].

• Child Restraint Systems: A car seat can be used onboard only if you buy the child a seat, and it cannot be placed in an aisle seat; one stroller and one car seat per child can also be checked free of charge [11].

• Neck Pillows: Southwest says neck pillows do not count toward the carry-on limit [1].

A pet carrier, on the other hand, does count: it is either your carry-on bag or your personal item [1].

1. Avoid “Over-Stuffing”: A soft-sided bag that should fit can stop fitting if it is packed so full that it bulges. If it doesn’t slide under the seat easily, you may have to move it to the overhead bin or check it.
2. The “Squish” Test: Choose a soft-sided bag over a hard-shell case: Southwest itself recommends soft-sided pet carriers because under-seat space varies [5]. A soft bag adapts to a tight space, but do not count on squeezing in a bag that is clearly too big.
3. Keep Essentials Accessible: Place your charging cables, headphones, and airline baggage fee documentation in the outer pockets so you don’t have to pull the entire bag out during the flight.
4. Power Bank Placement: Keep your one power bank (up to 100 watt-hours) in your personal item, never in the overhead bin; while you use it, it must stay visible, and it cannot be charged from the seat’s power outlet [10].

Core Rules

• Dimensions: No published personal-item size: it must fit under the seat in front of you. Carry-on: 24″ (L) x 16″ (W) x 10″ (H), wheels and handles included.
• Weight: No published limit, but Southwest decides what can go in the cabin.
• Allowance: One personal item plus one carry-on bag per passenger; a pet carrier counts as one of them.
• Checked Bags: Not free on most fares: $45 for the first and $55 for the second on Basic, Choice and Choice Preferred fares for U.S. mainland travel booked from April 9, 2026 [2].

Action Plan

1. Measure Your Bag: Do not rely on “standard” labels; use a measuring tape to check the length, width, and height of the packed bag (including handles and pockets).
2. Select Soft-Sided Luggage: Choose backpacks or duffels over rigid bags for better flexibility under the seat.
3. Identify Your Boarding Group: If you board in a late group (Basic fares board in Group 8), prioritize fitting everything essential into your personal item, as overhead bin space may be gone by the time you board [8].
4. Confirm Seat Location: If your bag is a tight fit, avoid an aisle seat when you choose your seat; Southwest says under-seat space may be more limited there [5].

Measuring your packed bag and choosing your seat with it in mind makes a “gate-check” surprise much less likely, allowing you to focus on your travel rather than your luggage.