Carry-On Size Checker

How to use the carry-on size checker

Measure your bag at its very widest points — over the wheels, over the handles, and over any pockets that bulge when it’s packed. Gate agents and the metal sizer bins measure the bag as it actually is, not the trimmer number on the manufacturer’s spec sheet, which usually leaves out the wheels. A 21-inch “carry-on” often measures 23 inches with its wheels and feet, and that is the number that gets it gate-checked.

Enter the three measurements in any order — length, width, height, it doesn’t matter. The checker sorts your bag’s sides and the airline’s limit from largest to smallest and compares them in order, so a bag that’s within the limit will pass however you type it in, and a bag that’s too big gets caught even if you enter the long side last. This mirrors what actually happens at the gate: a bag either drops into the sizer in some orientation or it doesn’t.

Pick your airline’s limit from the list. Most US major airlines share the same 22 × 14 × 9 inch standard; Southwest and a few others allow a more generous 24 × 16 × 10. The presets cover the common cases, and there’s a Custom option for anything else — budget European carriers, regional jets, or a specific fare class. When you’re flying an airline that isn’t listed, look up its exact limit and use Custom; the airline-limits table further down is a starting point, but carriers change these and enforce them differently.

The verdict is pass or fail, plus a line for each side so you can see exactly where an over-size bag is too big and by how much. If it’s over by half an inch on one side, you might fix it by repacking so the bag isn’t bulging, or by flying an airline with a roomier limit. If it’s over by two inches, it’s the wrong bag for that carrier and no amount of squeezing will help — plan to gate-check it or pick a smaller bag.

Two cautions the size check can’t see. First, many airlines also enforce a weight limit on carry-ons (common outside the US, and on budget carriers everywhere), and a bag that fits can still be too heavy. Second, the cheapest fares — Basic Economy in the US, the base fares on budget airlines — often don’t include a full-size carry-on at all, only a small personal item under the seat. Fitting the size limit doesn’t mean your ticket lets you bring it.

The formula

There’s no arithmetic to round here — the question is whether your bag fits inside the airline’s box in some orientation. The checker answers it the way a sizer bin does, by comparing the biggest side to the biggest side:

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

Worked example with the defaults — a 22 × 14 × 9 inch bag against the 22 × 14 × 9 US-majors limit: sorted, both are 22, 14, 9, so each side ties its limit and the bag just fits. Its linear measure is 22 + 14 + 9 = 45 inches. Bump the longest side to 23 and the comparison becomes 23 vs 22 on the top side — over by one inch — so it fails, even though linear inches (46) might look fine.

Sorting both sets is what makes the order of your measurements irrelevant: a bag entered 9 × 22 × 14 sorts to the same 22, 14, 9 as 22 × 14 × 9 and gets the same verdict. Linear inches is shown for reference, but most airlines enforce the three individual dimensions, not the sum — a bag can be under a linear total and still be too long on one side.

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