If your carry-on is 1 inch too big, you are essentially at the mercy of the gate agent's discretion, which has become much stricter in 2026. Most major airlines (Delta, United, American) have a standard limit of 22 x 14 x 9 inches. If your bag looks "bulky" or is expanded using the outer zipper, an agent may ask you to place it in the metal "sizer" box. If it doesn't fit—even by that one inch—you will likely be forced to gate-check the bag. On full-service carriers, they might do this for free if the flight is crowded, but on budget airlines like Frontier or Spirit, failing the sizer test results in a "gate bag fee" that can cost $100 or more. Hard-shell suitcases are the most "at risk" because they cannot be squished to fit. Soft-sided bags sometimes get a pass if they aren't fully packed, as you can physically force them into the dimensions. To be safe, always measure your bag including the wheels and handles, as those are the parts that usually catch on the sizer's frame and cause the "too big" verdict.