A linear inch is a measurement used in the travel industry to determine the size of luggage. A piece of luggage’s measurement in linear inches equals the sum of the lengths of its width, height and depth in inches. According to the Federal Aviation Administration, most airlines allow you to carry on a bag that is up to 45 linear inches. Carry-on baggage is luggage that you can carry onto a plane and keep with you during a flight. If your piece of luggage is larger than 45 linear inches, you may have to check your bag, which will be unavailable to you during flight.
Use a tape measure to measure the height in inches of a piece of luggage that you want to carry on an airline.
Measure the width in inches of the piece of luggage.
Measure the depth in inches of the piece of luggage.
Calculate the sum of the bag’s height, width and depth in inches. For example, calculate the sum of 22 inches in height, 14 inches in width and 9 inches in depth. This equals 45 linear inches, which means you can carry on this piece of luggage on most airlines.