Carry-on luggage size by airline

American allows one carry-on of up to 22 x 14 x 9 inches, plus one personal item of up to 18 x 14 x 8 inches. The carry-on allowance applies in all cabins, including Basic Economy on American - which is a meaningful difference from United and Delta, where Basic Economy strips the carry-on out entirely on most domestic routes.

American's personal item allowance is among the more generous published figures at 18 x 14 x 8, matching Spirit and Frontier. If you fly American often, that is a real planning advantage: an 18-inch under-seat bag is large enough to work as a genuine second bag rather than a laptop sleeve.

Delta caps individual dimensions at 22 x 14 x 9 inches (56 x 35 x 23 cm) and also applies a 45 linear inch total - length plus width plus height. In practice the two constraints agree, since 22 + 14 + 9 is 45 exactly, so a bag that passes the individual measurements passes the linear one too.

Delta publishes no dimensions for the personal item. The requirement is that it fits under the seat in front of you, and the page lists examples - a purse, briefcase, small backpack, camera bag, diaper bag or laptop bag. That vagueness cuts both ways: there is no number to fail against, but there is also no number to appeal to if an agent decides your bag is too big.

United allows 22 x 14 x 9 inches (56 x 35 x 23 cm) including handles and wheels, with a published personal item limit of 17 x 10 x 9 inches (43 x 25 x 22 cm). That personal item figure is the tightest of the eight carriers here, and it is the one to design your under-seat bag around if United is your regular airline.

United Basic Economy on most domestic routes includes the personal item only. A full-size carry-on brought to the gate on that fare gets checked for a fee. Check the fare rules on your specific ticket rather than the general baggage page - the allowance is set by fare class, not by airline.

Southwest publishes the most generous carry-on allowance of any major US carrier: 24 inches long by 16 wide by 10 high, with wheels, handles and attachments counting toward the measurement. That is two inches longer, two wider and one taller than the industry standard - a genuinely different bag size, not a rounding difference.

If you fly Southwest most of the time, the extra room is worth buying for. If you fly Southwest sometimes and other carriers the rest of the time, do not - a 24-inch bag is oversized on every other airline in this table, and you would be optimizing for the trip you take least often. Buy to the strictest limit you fly against regularly.

Southwest does not publish personal item dimensions; the requirement is that the item fits under the seat in front of you.

JetBlue publishes 22 x 14 x 9 inches (55.88 x 35.56 x 22.86 cm) for the carry-on and 17 x 13 x 8 inches (43.2 x 33 x 20.32 cm) for the personal item, including wheels and handles. JetBlue is one of the few carriers to publish personal item dimensions to the centimeter, which makes it easy to check a bag's spec sheet against the rule before buying.

Note the shape of that personal item allowance: 13 inches wide but only 8 deep. Wide, flat bags clear it comfortably; chunky cube-shaped backpacks often do not, even when their stated volume is modest.

Alaska allows one bag of no more than 22 x 14 x 9 inches, or 45 linear inches, including wheels and handle. Alaska's own guidance is explicit that expandable pockets count toward the measurement as well - so if your bag has an expansion zip, measure it zipped shut and then resist using it on the way home.

Alaska publishes no personal item dimensions, listing categories instead - a purse, briefcase or laptop bag - that must fit under the seat.

Frontier allows a carry-on of 24 x 16 x 10 inches and up to 35 lb, and a personal item of 18 x 14 x 8 inches and up to 35 lb, both including handles, wheels and straps. Frontier is one of the few US carriers to publish a carry-on weight limit at all, and it is the figure most people miss.

The generous dimensions are deceptive. On an ultra-low-cost carrier the carry-on is usually a paid add-on, and the personal item is the only free allowance - which is why the 18 x 14 x 8 figure matters far more here than the 24 x 16 x 10 one. Gate sizers are used, and they are used consistently.

Spirit publishes 22 x 18 x 10 inches (56 x 46 x 25 cm) for the carry-on and 18 x 14 x 8 inches (45 x 35 x 20 cm) for the personal item, including handles and wheels. The carry-on shape is unusual - the same 22-inch length as the standard, but far deeper and wider.

As with Frontier, the free allowance on most Spirit fares is the personal item only, so the 18 x 14 x 8 figure is the one that decides what you can bring without paying. Bags built specifically to that dimension have become a product category of their own, and they are worth considering if ultra-low-cost carriers are a regular part of how you travel.

There is no global standard. IATA has published a suggested cabin bag guideline in the past, but it is advisory and airlines are free to ignore it - and most do. The practical pattern outside the US is that dimensions are broadly similar to the 22 x 14 x 9 standard, sometimes a centimeter or two tighter, but a weight limit is added, and it is enforced.

Cabin bag weight limits of 7 to 10 kg are common on European, Asian and Middle Eastern carriers. That changes the buying calculation completely: on a carrier that weighs cabin bags, an empty 9 lb hardside suitcase has already consumed more than half of a 7 kg allowance before you pack anything. If you fly internationally on carriers that weigh, the empty weight of the bag is the most important number on its spec sheet.

The other international quirk is the long-haul connection. A bag that cleared the limit on your transatlantic leg may be measured again, against stricter rules, by the regional carrier operating your connecting flight. On a single ticket that is still your problem to solve at the gate.

Yes, on every carrier in this table. Southwest, Alaska, Frontier and Spirit state it explicitly; the others measure at the bag's widest points, which amounts to the same thing. Alaska additionally names expandable pockets.

This is where most gate disputes originate. A soft bag with a 22-inch body and a 1.5-inch wheel assembly is a 23.5-inch bag as far as the airline is concerned. Softside bags have an advantage here in that they compress into a sizer under a firm push, which is not a rule you can rely on but is a real difference in practice - see hardside vs softside luggage for where that flexibility does and does not help.

If you want to be certain, measure your packed bag at home with a tape, at its widest points, and compare it against the strictest airline you fly. A luggage scale is worth having for the same reason on carriers that weigh cabin bags.

Knowing the rule only helps if the next step is easy. These are the pages where we apply it:

• Best carry-on luggage - the main shortlist, every pick checked against the 22 x 14 x 9 standard.
• Best underseat carry-on bags - for the trips where the personal item is the whole allowance.
• Best personal item bags - sized for the under-seat space, including the 18 x 14 x 8 shape.
• Best budget carry-on luggage - the same constraint at a lower price point.
• Best travel backpacks - if you would rather carry than roll, and want to clear the same limit.