If you’re a former front-row kid who pushes your glasses up the bridge of your nose, checks the carry-on size restrictions for your airline, unfurls your measuring tape to compare against your own suitcase, and then worries endlessly about the half-inch difference, I get it. This is me; I am you. And if the slew of Redditors writing panicked pre-trip posts about their own luggage dimensions are any indication, we’re not alone.Here’s the problem we can’t wrap our heads around: Many airlines’ size restrictions for carry-on suitcases are smaller than many of the carry-on suitcases available for sale. This includes the carry-on suitcases that Wirecutter has tested and recommends.What gives? Is everyone just a half-inch and one meticulous gate agent away from shelling out big bucks for an oversize-bag fee?To get to the bottom of the problem, I asked my Denver-based colleague Elissa Sanci to visit the Denver International Airport with two of our carry-on picks, fully packed, to see if they would fit in the sizers for a slew of domestic and international airlines. The results: It’s complicated.