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.

Here's the problem by the numbers: Many bigger carry-ons, such as Away's The Bigger Carry-On, which measures 22.7 by 15.4 by 9.6 inches, are larger than the stated allowable carry-on size for most major US airlines, which is commonly 22 by 14 by 9 inches, though it varies by airline.

At the airport, we focused our attention on the two Away carry-ons because they're our top pick for hard-sided luggage and a prime example of a brand that offers both a larger and a smaller carry-on. To double-check Away's listed specs, I asked several people to independently measure their Away luggage. Thanks to the curved edges and protruding handles, this task was much harder than it seemed. ("Am I stupid? Why can't I do this?" one volunteer wondered. "Like measuring coastline," another said.) Though no one got the exact same result, their measurements were in the ballpark of Away's own.

At the airport, Elissa found that the sizers were often slightly roomier than the dimensions that the carrier listed online, and that two carriers with the same listed dimensions didn't always have the same-size sizers. Despite being technically too big for many US airlines on paper, Away's The Bigger Carry-On slid into every sizer we tried for a US-based airline. The fit wasn't always perfect, however -- while the frame always fit, the wheels occasionally overhung slightly.

On the other hand, the smaller standard Away The Carry-On, which measures 21.7 by 14.4 by 9 inches, fit easily into every US-based airline sizer we tried. But we don't think that means you should necessarily ditch your bigger carry-on for a smaller one just yet.

When I surveyed eight Wirecutter staffers who own Away's The Bigger Carry-On, none of them reported ever getting dinged with an oversize-bag fee while traveling with it. "Never in all my five-plus years with it," newsletter director Sofia Sokolove told me, "despite stuffing it to the gills." Deals writer Kaitlin Mahar told me that she has had to gate-check her Away Bigger Carry-On because it was too big, but she has never had to pay for it.

"Gate-checking is, in most cases, not a big deal!" Wirecutter carry-on guide writer Kit Dillon reminded me. "Your bag will likely come out right on the concourse as you disembark." (It's also possible that the bag will get gate-checked regardless of size, for reasons outside your control.)

Kit has also found that tiny infractions often go unpunished as long as the frame of the luggage fits in the sizer. He has personally traveled with our soft-sided carry-on pick, the Travelpro Platinum Elite, on more than 50 flights (mostly on US-based airlines) without issue. That carry-on's listed length (23.5 inches) is even longer than that of Away's The Bigger Carry-On, due to a protruding handle. Still, over 50 flights or so, he hasn't found a gate agent yet who is so strict that he has gotten charged for his bag.

But some domestic airlines are known for being sticklers, with a few budget airlines offering incentives for gate agents who flag oversize bags during boarding. Frontier reportedly paid gate agents $10 for each oversize bag they clocked; employees earned over $23 million in a five-year period. (Luckily, Away's The Bigger Carry-On fit in Frontier's generous sizer during our testing -- though that doesn't mean your bag would necessarily comply with the airline's carry-on weight limit of 35 pounds.)

Note that some budget airlines don't offer any free suitcases on their flights at all and have similar fees for carry-ons and checked bags -- which means you can just check your bag if you fear being charged for it. (Worried about checking? Our travel team is all for it.)

You Can Stop Stressing About Your 'Oversize' Carry-On