The following are the airline carry on luggage size requirements allowed today. Note that these can change anytime. You should check with the airline to be sure.
In Air France the maximum dimensions allowed are 22″ x 14″ x 9″ per passenger. You are also allowed to carry a briefcase, laptop computer or purse. At Air Tran Airways it is 55 linear inches. At Alaska Air/Horizon it is 24″ x 17″ x 10″. For American Airlines, the limit is 45 linear inches (L+W+H). At America West, the limit is 51 linear inches (L+W+H). The maximum allowable for British Airways is 22″ x 16″ x 8″.
At Continental it is 51 linear inches (L+W+H). Delta Airlines allows 22″ x 14″ x 9″ carry on bags. That is also the same dimensions allowed at Northwest Airlines. At Southwest Airlines it is 24″ x 16″ x 10″. If you are boarding Spirit Airlines, the airline carry on luggage size requirements is 22″ x 13″ x 10″. At United Airlines it is 22″ x 14″ x 9″, while at US Airways it is 24″ x 16″ x 10″. At Virgin Atlantic it is 22″ x 14″ x 9″.
About Luggage Policies
When an airline uses total numbers like 45, 51, 55 etc, it refers to the height, width and length of the unit. For example, 45” is 22 x 14 x 9. Some airlines are very strict about this. A slight deviation from these measurements can be cause for rejection.
Also remember that not all items being sold as carry-on are acceptable. Some of them are over the limits imposed by airlines, so you cannot use them. As the examples above show, most allow 45” but there are a few that let you take 55”.
Few stores will tell you or know if their bags are acceptable in airlines. Furthermore, the measurements they provide can be misleading or wrong. Frequently, the dimensions given are for the main compartment interior.
The assumption is the external pockets do not add to the thickness. They don’t take into account the fact that those pockets will be filled. Carry handles and wheels are also not factored in the measurements.
Even if you meet airline carry on luggage size requirements, there is no guarantee it can fit under the seat fronting you. Sometimes this is needed in case there is not enough space. The problem is the space there is getting smaller, so check the airline specs thoroughly first.