The maximum size most airlines allow for carry-on luggage in the United States is 45 linear inches, including handles and wheels, according to the Federal Aviation Administration. This means that in total, the height, weight and depth measurements of the bag cannot exceed 45 inches.
To be allowed on a plane, a piece of luggage must fit easily into the bag sizers found near the check-in counters at the airline's airport terminal. In addition to the 45-inch restriction, some airlines also place limits on the length of any one dimension.
Most airlines allow passengers one carry-on bag and one personal item free of charge. The second item, which might be a purse, briefcase or laptop bag, must fit under the seat in front of the passenger.