When you review the allowed size limit for carry-on bags, you’ll usually see it displayed as L x W x H. The first number is the longest edge, the second number is the “width” or medium-sized edge, and the final number is what would generally be referred to as the depth, but it is the shortest edge. Make sure you measure each dimension at its widest point. For example, make sure when measuring that you include wheels or handles to assure no problems upon check-in.