Remember these numbers: 22, 9, 14. They're not the winning numbers in a Pick 3 lottery or the combination to a safe full of jewels. Rather they're the maximum allowable dimensions in inches (height x depth x width*) for carry-on luggage on most U.S.-based airlines.
To avoid having to check luggage you intend to bring inside the cabin, use a bag that conforms to the strictest rules in the industry. Right now, for U.S. carriers, those are the ones set by American Airlines, Delta Airlines, and United Airlines. (U.S. Airways, now merged with American, has the same restrictions, as does Hawaiian, but with a 25-pound maximum weight.)
How do you measure a bag's dimensions? Place the bag in the upright position with wheels on the floor and its front facing you. The bag may not exceed 22 inches high, 9 inches deep (front to back), and 14 inches wide (side to side), including wheels, handles, and pouches. That's 45 linear inches—22+9+14.
Some airlines permit larger carry-ons:
In addition to the carry-on item, one "personal" item is permitted inside the cabin, as well as various "exempted" items.
Personal items include a purse, briefcase, tote bag, camera bag, laptop computer, or small backpack, and must fit beneath the seat in front of yours.
United limits personal items to 17x9x10 inches. American Airlines (including U.S. Airways) does not provides specific dimensions, but simply states that the personal item must be smaller than your carry-on bag and must fit under the seat in front of you. Delta says that the item has to be "of a similar or smaller size" than a purse, briefcase, camera bag, or diaper bag.
If you are sitting in a bulkhead seat—with no seat in front of you—you can still keep your personal item on the floor at your feet during flight; during takeoff and landing the flight attendant will stow it in a safe area.
Exempted items might include a jacket/coat, hat, book or newspaper, pillow, blanket, umbrella, walking stick, cane, duty-free purchases, medical equipment in a separate bag, assistive devices, an approved child-safety seat, and a small bag of snacks or drinks purchased in the gate area.
If you plan to bring a diaper bag or a pet carrier on board, check the rules as some airlines designate these items as carry-on bags; others consider them exempted items.
If you're flying on a commuter flight or an affiliated regional airline, such as American Eagle, Delta Connection, Horizon Air, SkyWest, and United Express, note that because these aircraft often are smaller, a bag that would otherwise meet carry-on requirements might be gate-checked—the ground crew will take it from you right before you board the plane and stow it in the luggage hold.
Knowing the rules won't cover you 100 percent, though. Airlines can impose further restrictions, even after boarding has begun.
Finally, be aware that airlines stealthily change their bag-size rules. Even the travel expert George Hobica got caught unaware when he recently tried to board an American Airlines flight with a bag that formerly had been compliant but out of the blue was no longer. Our advice: Check your carrier's rules every time you fly.
Height is the measurement from the floor, including wheels, to the top of the handle in its lowered position. Depth is the measurement from front to back. Width is the measurement from side to side.