U.S. airlines collected $6.8 billion in checked baggage fees in 2026. That number has pushed more travelers toward carry on-only strategies — but the problem nobody talks about is that many popular carry on bags sold at major retailers exceed at least one major airline’s maximum dimensions. You can buy a bag that flies fine on Southwest but gets gate-checked on American every single time. This guide names specific bags, gives you exact dimensions, and explains the mechanics behind airline size enforcement so you stop guessing and start packing with confidence. How Airline Size Rules Actually Work — and Where…