Check your airlines faq to see the measurements of the largest bag you can bring. If you fly multiple different airlines, check the ones you fly most frequently and choose a size bag that will satisfy all the airlines requirements.
[header] How to pack your carry on bag [title] Pick the right bag. [step] Make sure it's durable, easy to carry, and that it can hold all of your necessary items. More importantly, make sure it meets your airline's size requirements.