Personal Item Size by Airline

A backpack counts as a personal item on every US carrier, provided it fits under the seat. The problem is that the published box varies by nearly double.

By Sawyer V.Last updated September 3, 2026

We have not tested this gear. Every figure here is compiled from published manufacturer specifications and published airline policies, and the arithmetic is public so you can check it. This page contains affiliate links — see the affiliate disclosure.

Yes — a backpack counts as a personal item on every US airline, as long as it fits under the seat in front of you. The published box varies more than the answer suggests: United allows 17 × 10 × 9 in while American, Frontier and Allegiant all allow 18 × 14 × 8 in, which is roughly 30% more volume. Four US carriers publish no personal-item dimensions at all.

US carriers. Published maximum personal-item dimensions in inches, wheels, handles and straps included.
Airline	Published personal-item limit	Carry-on limit	Source	Checked
American AirlinesAA	18 × 14 × 8 in	22 × 14 × 9 in	aa.com	2026-09-03
Delta Air LinesDL	Not published	22 × 14 × 9 in	delta.com	2026-09-03
United AirlinesUA	17 × 10 × 9 in	22 × 14 × 9 in	united.com	2026-09-03
Southwest AirlinesWN	18.5 × 13.5 × 8.5 in	24 × 16 × 10 in	support.southwest.com	2026-09-03
Alaska AirlinesAS	Not published	22 × 14 × 9 in	alaskaair.com	2026-09-03
JetBlueB6	17 × 13 × 8 in	22 × 14 × 9 in	jetblue.com	2026-09-03
Frontier AirlinesF9	18 × 14 × 8 in	24 × 16 × 10 in	faq.flyfrontier.com	2026-09-03
Allegiant AirG4	18 × 14 × 8 in	22 × 16 × 10 in	allegiantair.com	2026-09-03
Hawaiian AirlinesHA	Not published	22 × 14 × 9 in	hawaiianairlines.com	2026-09-03
Breeze AirwaysMX	17 × 13 × 8 in	22 × 14 × 9 in	flybreeze.com	2026-09-03
Sun Country AirlinesSY	17 × 13 × 9 in	24 × 16 × 11 in	suncountry.com	2026-09-03

Every row cites the carrier’s own published policy and carries the date we checked it. Where a carrier publishes no dimensions, the rule is simply that the item fits under the seat in front of you.

The answer behind the answer

“Does a backpack count as a personal item?” is really two questions wearing one coat. The first — is a backpack an allowed type of personal item — has an easy yes: every carrier in the table above names a backpack explicitly, alongside a purse, a laptop bag or a briefcase. The second question is the one that gets people gate-checked: does your particular backpack fit the box?

Most travel backpacks do not. A 40 L carry-on pack is typically 22 × 14 × 9 in — that is a carry-on, not a personal item, and it is over United’s 17 × 10 × 9 in box on every dimension. What fits under a seat is a 18–30 L bag, and we rank the ones that do against these limits specifically.

The spread is bigger than the carry-on spread

Carry-on limits vary by about 39% in volume across the US market. Personal-item limits vary by more, and in a less predictable direction — the carrier with the tightest personal-item box is not a budget airline, it is United.

Published personal-item boxes, grouped by dimension. Volumes are the product of the three published maxima.
Published box	Carriers	Volume	Fits a 30 L soft bag?
18 × 14 × 8 in	American, Frontier, Allegiant	2,016 in³	Yes — this is the box the 18×14×8 bags are built to
18.5 × 13.5 × 8.5 in	Southwest	2,123 in³	Yes, with a little margin
17 × 13 × 8 in	JetBlue, Breeze	1,768 in³	Only just — an 18 in bag is over on length
17 × 13 × 9 in	Sun Country	1,989 in³	Only just, same length problem
17 × 10 × 9 in	United	1,530 in³	No — the tightest box in the US market
Not published	Delta, Alaska, Hawaiian	—	Rule is that it fits under the seat

United’s box has 24% less volume than American’s. If you fly both and want one bag that works on both, the bag has to fit United — which in practice means a pack around 20 L rather than 30 L.

The four carriers that publish nothing

Delta, Alaska and Hawaiian publish no personal-item dimensions. Their rule is the physical one: the item must fit under the seat in front of you. That sounds looser and in practice it usually is, but it is also unappealable — there is no published figure to point at if a gate agent decides your bag does not fit.

Under-seat space is not a constant either. It varies by aircraft, and a bulkhead row or an exit row often has no under-seat storage at all, which is worth knowing before you choose the seat that comes with the legroom.

The free-bag strategy on paid-carry-on carriers

On Frontier, Allegiant, Breeze and Sun Country the overhead bag costs money and the personal item does not. That turns the personal-item box into the interesting purchase: Frontier and Allegiant both publish 18 × 14 × 8 in, and a soft bag built to exactly that carries around 30 L — enough for four or five days if you pack deliberately.

Buy the box, not the liters. A bag advertised at 30 L that measures 19 in long is not a personal item anywhere.
Soft bags grow. A structured 18 × 14 × 8 in bag stays that size; a soft duffel packed to bulging does not. Depth is the dimension that goes first.
Wheels count. Frontier and Allegiant both state that handles, wheels and straps are included in the measurement.
United is the constraint. If United is in your rotation, size for 17 × 10 × 9 in and everything else is easy.

Per-carrier notes

American Airlines: American measures the full outside size of a carry-on, wheels and handles included.
Delta Air Lines: Delta also caps the carry-on at 45 linear inches (length plus width plus height). It publishes no personal-item dimensions; the rule is that the item fits under the seat in front of you.
United Airlines: United's personal-item box is the tightest of the big three US carriers. Basic Economy on some domestic routes allows the personal item only.
Southwest Airlines: The roomiest published carry-on box of any major US carrier. A bag bought to fill Southwest's allowance will not fit most of the others.
Alaska Airlines: Alaska publishes no personal-item dimensions; the item must fit under the seat ahead of you.
JetBlue: JetBlue states plainly that it has no carry-on weight restriction, but you have to lift the bag into the bin yourself.
Frontier Airlines: One of the few US carriers publishing a carry-on weight limit, and one that charges for the overhead bag. Frontier prints the personal item as 14 in high by 18 in wide by 8 in deep.
Allegiant Air: Allegiant states the measurement includes wheels, pockets, handles and decorations. Only the personal item is free.
Hawaiian Airlines: The tightest published carry-on weight limit in this table, at 25 lb. Several hardside carry-ons weigh a quarter of that empty.
Breeze Airways: The overhead bag is bundled into the Nicer and Nicest fares or bought separately. The personal item is included on every fare.
Sun Country Airlines: A generous published box, but the overhead bag is a paid add-on and carries a 35 lb cap.

Bags whose published dimensions fit a personal-item box

Ranked by how many US carriers' published personal-item limits each bag satisfies. Note how few clear United's 17 × 10 × 9 in box — that is the constraint worth designing your purchase around.

Narwey Foldable Personal Item Bag (18 × 14 × 8 in)
18 × 14 × 8 in · fits 3 of 11 US carriers
Frontier and Allegiant flyers refusing to pay for an overhead bag
Check price#ad How we earn
MATEIN Professional Travel Laptop Backpack
18 × 14 × 8 in · fits 3 of 11 US carriers
Working travelers whose personal item has to be the laptop bag
Check price#ad How we earn

Full rankings: carry-on luggage · carry-on backpacks · carry-on duffels

Common questions

Does a backpack count as a personal item?

Yes, on every US airline, provided it fits under the seat in front of you. Every carrier we track names a backpack explicitly as an acceptable personal item. The constraint is size, not type: United’s published box is 17 × 10 × 9 inches, while American, Frontier and Allegiant publish 18 × 14 × 8 inches.

Is a backpack a personal item or a carry-on?

It depends entirely on its dimensions. A daypack of roughly 20 liters is a personal item on every carrier. A 40 liter travel pack measuring 22 × 14 × 9 inches is a carry-on — it is the same size as a wheeled cabin bag and goes in the overhead bin, not under the seat.

Does a backpack count as a personal item on United?

Yes, if it fits United’s published 17 × 10 × 9 inch box. That is the tightest personal-item limit of any US carrier we track — 24% less volume than American’s — so many bags sold as “personal item” bags, particularly the 18 × 14 × 8 inch ones, are over it.

What is the personal item size for Frontier and Allegiant?

Both publish 18 × 14 × 8 inches including handles, wheels and straps. Frontier prints it as 14 inches high by 18 inches wide by 8 inches deep, which is the same box in a different order. On both carriers the personal item is free and the overhead carry-on is a paid extra.

Which airlines do not publish a personal item size?

Delta, Alaska and Hawaiian publish no personal-item dimensions. Their rule is that the item fits under the seat in front of you, which is generally more generous in practice but gives you nothing to point at if a gate agent disagrees.

Can I bring a purse and a backpack?

Not as two separate free items on most carriers. The standard allowance is one carry-on plus one personal item, and a purse and a backpack are two personal items. The usual workaround is to put the smaller bag inside the larger one before boarding.