Airlines check cabin bags against their published limit, often in a metal sizer at the gate. The way to avoid a surprise is to measure your bag the same way, at home, once it is packed.
Measure the outside, wheels and handles included
Stand the bag upright and measure its three outer sides: height from the floor to the top of the handle housing, width across the widest point, depth from the back to the front pocket. Include wheels, feet, handles and pockets. Air Corsica and Peach, for example, state in their rules that wheels and handles count in the size. Wizz Air is an exception: it does not count wheels and handles in its limit, but the wheels may not add more than 5 cm.
Measure it packed, not empty
A soft bag or a backpack grows once it is full. A bag that measures 20 cm deep when empty can gain a few centimetres with clothes inside, and depth is usually the side that grows. Close every pocket and measure the bag as you will carry it.
Compare the longest side with the longest limit
A bag can be turned to fit a sizer, so the order of the figures does not matter. Sort your three sides from longest to shortest, do the same with the airline's limit, and compare them in pairs. Our checker does this for you.
Check the total when an airline publishes one
Some airlines give a sum instead of, or as well as, three sides. Oman Air, for example, allows a cabin bag whose length, width and height add up to 115 cm or less. Add your three sides and compare the result with that total.
Convert units without rounding up
A US carry-on of 22 in is 55.9 cm, not 55 cm. When you convert, keep the decimal: a bag of 22 × 14 × 9 in is 0.9 cm over a 55 cm limit.
Weigh the bag on its own
A hand-held luggage scale gives the most direct reading. Without one, weigh yourself on a bathroom scale with and without the bag, and take the difference. Check whether your airline counts the cabin bag and the personal item together, as several airlines set one weight for both.