55 is the max carry-on size, but I'm not sure if it fits in the overhead compartments if it's full. I've only travelled with mine once, and then I had to take it under the seat in front of me because it looked to big for the overhead compartment. If I could choose again I'd rather buy a 50 with shoulder strap, because my 55 gets really heavy some times and then the shoulder strap give me marks where it have been, and other times I don't pack it more than half-full, and then it looks kinda ugly. But I still love it though, so good luck with your keepall no matter what you decide on!