If you've ever struggled to pack your carry-on on a flight so that all your essentials are within reach, only to find out at the gate that it's too big and have to be checked, then you know the importance of bag size information. The carry-on baggage rules for major U.S. airlines are very strict and can be found on each airline's website, but most people don't fully understand the rules or know if the bag they're using meets that standard. While there may sometimes be a little leeway, the overhead storage bins can only accommodate bags of certain sizes. If your bag is longer or taller and takes up more space than allocated, you screw up the algorithm and other people's bags won't fit.
The reason these rules seem flexible is that if you're on a flight that's not sold out, your gate agent may be more willing to let you board with a bag that's slightly larger than airline regulations, as long as it fits in the bin. However, if your flight is fully booked and most passengers are carrying carry-on luggage in addition to their personal belongings, you'll be less likely to sneak in a large piece of luggage. What's more, if you're on a crowded flight and are the last to board, you may be forced to check your bag, even if it's the right size , because there's no room left in the cabin.
The best way to ensure that you and your luggage arrive at the same place at the same time is to make sure your proportions comply with the requirements of the specific airline you're flying. Generally speaking, American Airlines allows economy luggage with a total length of 45 inches with no weight limit, as long as you can lift it overhead and put it in a storage compartment. An exception to this rule is if your flight is on a small aircraft and the crew decides at the last minute to force checked bags.
Of course, each airline has its own specific rules - and it's important to understand them if you plan to fly with them. Here are the details of domestic airlines:
JetBlue Airways
Your carry-on bag must be no larger than 22 inches x 14 inches x 9 inches, total dimensions including handles and wheels. JetBlue does not impose a weight limit on carry-on luggage, but you must be able to lift it overhead and into a storage compartment without assistance. You may also bring one personal item.
Delta Airlines
The dimensions of your bag must not exceed 22 inches x 14 inches x 9 inches, total dimensions including handles and wheels. Delta does not impose a weight limit on carry-on luggage on domestic flights, but you must be able to lift it overhead and into a storage bin without assistance. Before boarding, you can double-check that your luggage is the right size by placing it on the terminal's size guide.
United Airlines
The dimensions of your bag must not exceed 22 inches x 14 inches x 9 inches, total dimensions including handles and wheels. United Airlines does not impose a weight limit on carry-on luggage, but you must be able to lift it overhead and into a storage compartment without assistance. You can also bring one personal item and one approved duty-free item for free.
American airlines
The dimensions of your bag must not exceed 22 inches x 14 inches x 9 inches, total dimensions including handles and wheels. American Airlines does not impose a weight limit on carry-on luggage, but you must be able to lift it overhead and into a storage bin without assistance. American Airlines notes on its website that if you're flying on a particularly small plane, there may be more restrictions on what you can carry on, but you'll likely not be charged a checked fee.
Alaska Airlines
Due to the latest luggage size updates implemented in June 2019, your luggage must be no larger than 22 inches x 14 inches x 9 inches, total dimensions including handles and wheels. Alaska Airlines does not impose a weight limit on carry-on luggage, but you must be able to lift it overhead and into a storage bin without assistance. You can also bring one personal item, but it must fit under the seat in front of you.
