Why do the size limits of carry-on bags vary by airline and is there a size limit that will work for all airlines?

Each airline designs aircraft interiors according to their own specifications. This means the overhead compartments and under seat space will vary by airline and by type of aircraft. As a very general rule, if your baggage is no larger than the following dimensions it will be permissible on all major domestic carriers:

• Carry-on (overhead bin) – 9″ x 14″ x 22″
• Personal Item (under seat) – 9″ x 10″ x 17″

Keep in mind that some small regional aircraft may have more limited space and some seats on some aircraft may have a slightly smaller under-seat area due to seat structure or mechanics.