1. Why a carry-on gets stopped
Airlines use a sizing bin at the gate, and an oversized bag may be checked and charged extra.
Carry-on definitions differ between airlines and between cabins and fares on the same airline; budget fares usually come with stricter limits.
2. The most common reference standard
IATA recommends a carry-on size of 55 × 35 × 20 cm (about 21.5 × 13.8 × 8 in), roughly 110 cm in linear size.
That is an industry suggestion, not a mandatory standard. Most airlines adjust it, so check the operating airline's baggage page.
3. How to measure your bag
Measure the bag when it is full, including wheels, handles and outer pockets.
Use a soft tape along the longest points for length, width and height, then add them for linear size. Soft bags should fit the sizing bin when compressed.
4. Personal items and soft bags
Most airlines allow a personal item (backpack, handbag or laptop bag) in addition to the carry-on, but its size limit varies.
Soft bags are easier to squeeze into a sizing bin, but you may be asked to push them in completely, so do not rely on the nominal size alone.
5. Common mistakes
Common mistakes include buying by the bag's nominal size instead of measuring it, forgetting the height that wheels and handles add, mixing up linear size with single-edge limits, and checking one airline's standard against another flight.
Checks are stricter on busy days and full flights; leaving 1–2 cm of margin reduces risk.
6. Checklist before departure
Before departure: open the operating airline's page and confirm the allowance for your fare; measure the full bag and leave a little margin; screenshot the boarding pass and the airline's baggage rules for gate checks.