Kenzo is right 55 is the biggest possible to carry on, but I own 60. I personally don't think that the strap is very useful because when 60 is full it weighs about 18 kilos which is too heavy for me to carry on the shoulderJust curious... I have some travel coming up and would like to get a Keepall. What sizes do you love and find perfect?? And does anyone know which is the largest one that meets carry-on limits?