What constitutes a carryon?

"Some luggage sold as suitable for airline carry-on exceeds all airline size limits.Know what you can and can't carry on to your flight in advance." - The Travel Insider

What can you carry on the airplane?  With most US carriers you are allowed one piece of carry-on luggage plus a "personal item". The most important thing to know about your carry-on luggage is that it should in the neigborhood of  22" x 14" x 9" or smaller. The total dimensions (height+length+width) should equal no more than 45", but the bag must fit in the plane's overhead storage compartment. Odd shapes or overstuffed bags can cause problems. If in doubt, measure your luggage. Don't trust the label in the store - measure it.

The personal item can be a briefcase, camera bag, handbag, purse, small shoulder bag, laptop (in carry bag), other items not exceeding 36" in total dimension, reading matter, small book-bag style backpack, or umbrella. The personal item will need to fit under the seat in front of you on the plane.

Learn more about carry-ons here.