You may not have to use a tape or rule to measure the size of your carry-on luggage. A sight of it should tell you whether it’s okay or not.
Airlines allow one carry-on luggage and a laptop. The luggage should fit the overhead bin of the aircraft. The standard size of a piece of carry-on luggage is 9 inches x 14 inches x 22 inches (22 centimeters x 35 centimeters x 56 centimeters).
Smaller aircraft usually have smaller overhead bins which might not accommodate luggage of the standard size. Airlines check in such luggage at no additional cost to the traveler.
If you wish to carry your carry-on luggage with you at all cost, first consider the type of aircraft you are flying before choosing carry-on luggage.
Always show your carry-on bag at the check-in counter for the attendant to confirm that the size and weight are okay. The weight of a piece of carry-on luggage must not exceed 12kg.
Note that you will be forced to check in and pay for carry-on luggage if the size and weight exceed the airline’s limit. Always crosscheck with the airline to confirm the number of luggage and weight your ticket allows. Higher-level members of frequent flyer programs may qualify to check in additional luggage for free.