Linear inches

Linear inches, sometimes called linear centimeters outside the US, is the total you get by adding a bag's length, width and height together. Instead of publishing three separate maximum measurements, some airlines, especially for checked baggage and a few carry-on policies, set one combined number that the three dimensions must add up to or under.

This matters because two bags with the same linear total can have very different shapes. A tall, narrow bag and a short, wide bag might both add up to 45 linear inches, but only one of them might fit a particular overhead bin or a strict sizer frame at the gate. It is worth checking whether an airline uses linear inches or three separate maximum dimensions before assuming a bag will be accepted.

When comparing bags, look at both the linear total and the individual length, width and height, since product listings do not always show both. A common mistake is comparing a bag's linear inches to an airline's separate length and width and height limits, which are not the same measurement and cannot be checked against each other directly.