Nowadays airlines are more strict than ever when it comes to carry on baggage. To save money and charge more fees, airlines decreased dimensions of bags allowed on board:
1) Carry on bag
In 2015, TSA issued new maximum allowed dimensions of carry-on bags:
22 x 14 x 9 inches (56 x 35 x 22 cm)
However there are still some airlines, like Virgin America or Frontier Airlines, that allow bags up to 24 x 16 X 10 inches on board.
2) Personal Item
Majority of airlines also allow one personal item on board that is not bigger than 17 x 10 x 9 inches. Personal item should be able to fit under the seat in front of the passenger.
If you are still looking for a carry on that will be easy to carry and is within maximum allowed dimensions, check out the Prottoni Carry on Backpack. It has 41 L capacity, separate, zippered laptop compartment as well as hidden travel pocket for valuables.