Carry-On Size Checker

How to use the carry-on size checker

Measure your bag packed and at its very widest points, over the wheels, over the retracted handle and over any pocket that bulges once the bag is full. Gate agents and the metal sizer bins measure the object as it actually is, not the trimmer figure on the manufacturer spec sheet, which very often quotes the body of the case and leaves out the wheels and feet.

A bag sold as a 21 inch carry-on can easily measure 23 inches assembled, and that difference is what triggers a gate-check. Then enter the three numbers in any order at all.

The checker sorts your sides and the airline sides from largest to smallest and compares them in pairs, which is exactly what happens physically when you rotate a bag to drop it into a sizer, so a bag entered 9 by 22 by 14 gets the same verdict as one entered 22 by 14 by 9.

The most important thing to understand is that there is no universal cabin bag size, and there never has been. Most US majors converged on 22 by 14 by 9 inches, which is why so much luggage is built to it.

But Southwest and Frontier allow a roomier 24 by 16 by 10, Air Canada publishes 21.5 by 15.5 by 9, and European carriers publish in centimetres against different boxes again: Ryanair allows 55 by 40 by 20 cm for a cabin bag, while British Airways and easyJet allow 56 by 45 by 25 cm. Those are genuinely different shapes, not rounding differences.

The presets in this tool cover the common cases, and there is a Custom option for everything else. When you are flying a carrier that is not listed, look up its published figure and enter that rather than assuming a regional standard applies to it.

What counts as a free personal item?

Treat the personal item as a separate allowance with its own rules, because for a lot of tickets it is the only bag included.

In Europe, Airlines for Europe members agreed to implement a guaranteed free personal item of at least 40 by 30 by 15 cm, following the position agreed by member states on 5 June 2025, and rolled it out across the 2025 summer season; several carriers are more generous than that floor, with Ryanair at 40 by 30 by 20 cm and easyJet at 45 by 36 by 20 cm.

In the US there is no equivalent common standard, and published personal item figures range from 17 by 10 by 9 inches at United to 18 by 14 by 8 at American and Frontier, while some carriers publish no dimensions at all and simply require the bag to fit under the seat.

The formula, worked line by line

There is no arithmetic to round here. The only question is whether a rectangular bag fits inside a rectangular box in some orientation, and the answer does not depend on which side anyone chose to call the length.

Sort the three sides of the bag from largest to smallest, sort the three sides of the limit the same way, and compare them in pairs. The bag fits only if every one of its sides clears the limit side it is paired with.

That sort is what makes the order you type in irrelevant, and it mirrors the physical act of turning a case to drop it into a sizer bin.

Linear inches, the plain sum of the three sides, is shown alongside for reference only, because most carriers enforce three separate dimensions rather than a total. A bag can sit comfortably under a linear limit while being an inch too long on its longest edge, and it is the long edge that fails it.

sort the bag 3 sides, largest first
sort the limit 3 sides, largest first
fits = every bag side ≤ the limit side in the same position
linear inches = length + width + height

Try the same bag against a different carrier and the answer changes with no change to the bag. That 23 x 14 x 9 case fails the US majors limit but passes Southwest and Frontier at 24 x 16 x 10 with an inch to spare on every side.

Run it against Ryanair instead, whose limit is 55 x 40 x 20 cm or about 21.7 x 15.7 x 7.9 inches, and it fails twice over: 23 against 21.7 on the longest side and 9 against 7.9 on the shortest. This is the practical reason the tool asks which limit to use rather than assuming one, and the reason a bag that has flown for years can suddenly be refused on a different carrier.

Two limits sit outside the geometry entirely. Weight is the first: many carriers outside the US, and budget carriers almost everywhere, cap the cabin bag by mass as well as by size, so a bag that drops into the sizer can still be turned away, and this tool has no weight input at all.

Fare class is the second: domestic Basic Economy on United includes only a personal item, Frontier sells the cabin bag as an add-on, and Ryanair and Wizz Air require a priority product before a full-size bag reaches the overhead locker. Airline rules also change on their own timetable, so treat the table above as dated reference data and confirm the current allowance with your own carrier before you travel.

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