What Is a Carry-On Bag? Size, Type and Airline Rules
A carry-on bag is any bag within your airline's size limit that goes in the overhead bin. What counts, by type and by airline, checked September 2026.
The short answer
A carry-on bag is any bag, whatever its shape, that fits within your airline’s size limit and goes in the overhead bin. On most US carriers that limit is 22 x 14 x 9 inches (56 x 35 x 23 cm) including wheels and handles; Southwest allows a slightly larger 24 x 16 x 10 inches. A duffel, backpack, garment bag or soft-sided suitcase all qualify the same way a hard-shell case does, if the packed bag clears the size test. Anything smaller that fits under the seat instead is your separate personal item.
You’ve got two bags by the door, one headed for the overhead bin and one staying at your feet. The question of which is which usually shows up the night before a flight, not while you had time to check the airline’s page.
This works through what actually makes a bag a carry-on rather than a personal item, whether the type of bag matters, and where the size numbers come from, airline by airline. Every figure below is checked against the airlines’ own published pages and IATA’s baggage guidance as of September 2026.
What to check before you call something a carry-on
- A tape measure, not the dimensions printed on the bag’s spec tag, since wheels, straps and bulging outer pockets all count toward the limit
- The bag packed the way you’ll actually carry it, with wheels attached and any handle retracted
- Your fare class, since Basic Economy and Saver tickets on some airlines drop the carry-on to a personal item only
- Whether your trip includes an international or codeshare leg, where a partner airline’s limit can apply instead of the one you checked
- Whether the airline charges for a carry-on at all, since Frontier and Allegiant price it separately from the free personal item
Carry-on vs. personal item: the real difference
The split isn’t about bag design, it’s about where the bag goes. A carry-on is sized for the overhead bin; a personal item is sized to fit under the seat in front of you.
American Airlines caps a personal item at 18 x 14 x 8 inches, and JetBlue at 17 x 13 x 8 inches. Delta, Alaska and Southwest publish no fixed personal item dimensions at all, they just require that it fits under the seat.
That gap matters more than it looks. A backpack that’s too tall to slide under the seat still counts as a carry-on, not a personal item, even if you packed it thinking of it as your “small bag.”
Does the type of bag matter?
No airline restricts you to a rolling hard-shell case. A duffel, a backpack, a garment bag or a soft-sided suitcase are all treated the same as a hard-shell carry-on, provided the packed bag clears the airline’s dimensions.
Soft-sided bags actually have an edge at the gate sizer. A duffel or a fabric backpack compresses into the metal frame in a way a rigid hard-shell case cannot.
A bag that’s an inch over on paper sometimes still passes because of that give, where a hard-shell equivalent would not.
Is a duffel bag a carry-on?
Yes, as long as it’s packed within your airline’s carry-on dimensions, typically 22 x 14 x 9 inches on a US major. Most duffels run large enough once packed that they clear the personal item allowance and land in carry-on territory instead, so a duffel is more often the carry-on than the “small bag” underneath the seat.
The one place duffels get caught out is the linear-inch rule some airlines apply on top of the three individual measurements. A duffel’s bulging middle can add up even when its length, width and height each look fine on their own.
Are suitcases considered carry-ons?
Yes, hard-shell or soft-sided, wheeled or not, as long as the case fits the airline’s stated limit. The word “suitcase” carries no special status; a 20-inch hard-shell case and a soft duffel are judged by the exact same tape measure.
Watch the marketing label rather than trusting it. A case sold as a “22-inch carry-on” is describing its outer length only, not the combined linear-inch total some airlines enforce, and not every “underseat” suitcase actually fits every airline’s personal item allowance.
What is carry-on size, exactly?
In the US, 22 x 14 x 9 inches (56 x 35 x 23 cm) is the figure that matters, shared by Delta, American, United, Alaska and JetBlue. Southwest is the outlier at 24 x 16 x 10 inches.
IATA, the airline industry’s own trade body, recommends a smaller “Cabin OK” figure for international travel: 55 x 35 x 20 cm (21.5 x 13.5 x 7.5 in). That’s a guideline meant to fit on the widest range of aircraft worldwide, not a rule any single carrier is bound to.
It’s also smaller than every US major’s own limit. A bag built to the IATA guideline clears every domestic sizer with room to spare, while a bag built to the larger US standard can fail a stricter international carrier’s test.
Carry-on size and weight, by major US airline
| Airline | Carry-on max size | Weight limit | Bag type restriction |
|---|---|---|---|
| Delta | 22 x 14 x 9 in, 45 linear in | None | None, any type within size |
| American | 22 x 14 x 9 in | None | None; soft garment bag up to 51 in accepted |
| United | 22 x 14 x 9 in | None | None; Basic Economy drops it domestically |
| Alaska | 22 x 14 x 9 in | None | None |
| JetBlue | 22 x 14 x 9 in | None | None |
| Southwest | 24 x 16 x 10 in | None | None |
| Frontier | 24 x 16 x 10 in | 35 lb | None, but always a paid add-on |
This is a quick reference, not the full picture. Delta’s carry-on size, and every other major airline’s covers international carriers and every US major in one table.
Delta’s carry-on weight limit, and how other airlines compare goes deeper on the weight side, including the airports where even Delta does weigh the bag.
Weight limits: the exception, not the rule
Most US majors don’t weigh a carry-on at all. Delta, American, United, Alaska and JetBlue all set the same reasoning: if you can lift the bag into the overhead bin unaided, it passes, regardless of what’s inside it.
Frontier is the domestic exception, capping a carry-on at 35 lb on top of its size limit. Weight becomes the real test once you leave the US, where several international carriers cap carry-ons at 7 to 12 kg regardless of how well the bag fits the sizer.
That difference is covered in full in the weight comparison linked above.
What happens if your bag doesn’t qualify
A bag that fails the gate sizer doesn’t get a warning first, it gets gate-checked, usually for a fee that’s cheapest when paid at booking and most expensive at the gate itself. On United’s domestic Basic Economy, a gate-checked bag adds the standard checked fee plus a separate handling charge on top, not instead of it.
Enforcement isn’t perfectly consistent between flights. A bag that clears the sizer on one leg can get flagged on the next, particularly on a full flight where overhead space runs out before boarding finishes.
Your carry-on was stopped at the gate
- Ask which limit it failed, size or weight, since the fix is different for each
- If it’s weight on an airline that enforces one, move the heaviest items into your personal item before the bag is weighed again
- If it’s size, expect to gate-check it rather than repack on the spot, since overhead bin space at that point is usually already gone
- Ask what the fee covers before you agree to it, since a gate handling charge can apply on top of the standard checked-bag fee
- If your fare was Basic Economy or Saver, confirm with the agent whether your specific route qualifies for a carry-on exception before assuming it doesn’t
Frequently asked questions
In short
A carry-on is defined by size and stowage location, not by what kind of bag it is. Most US majors share the same 22 x 14 x 9 inch limit and set no weight restriction; Southwest and Frontier are the notable exceptions, and Frontier charges for the bag regardless of fare.
A duffel, backpack, garment bag or suitcase all pass the same test.
Rules change without much notice. If something here no longer matches what you were told at the gate, tell us and we will correct it.
Once the bag itself is sorted, the next practical question is usually what’s allowed inside it. Can you pack razors in a carry-on? and does deodorant count as a liquid for TSA? both cover what goes through security once your bag does.
If it turns out your bag is better off checked, Delta’s baggage policy, plus checked bags for every major airline covers that instead.
Sources
- TSA: Carry-on bag size restrictions, checked 2026-09-03
- TSA: What Can I Bring?, checked 2026-09-03
- IATA: Passenger Baggage Rules, checked 2026-09-03
- Delta: Carry-On Baggage, checked 2026-09-03
- American Airlines: Carry-on bags and size limits, checked 2026-09-03
- United: Carry-on Bags, checked 2026-09-03
- Alaska Airlines: Carry-on luggage size limit, checked 2026-09-03
- JetBlue: Carry-on Bags, checked 2026-09-03
- Southwest: Optional Travel Charges, checked 2026-09-03
- Frontier: Bag options, checked 2026-09-03
