Although maximum luggage size is dictated by the International Air Transport Association and, within the United States, the Federal Aviation Administration, the airline decides the maximum weight limits for carry-on bags and luggage. Carry-on luggage size allowances vary depending on whether a flight is domestic or international, which route you’re flying and the class in which your seat is located, so always check with the airline before leaving home to avoid a potentially expensive surprise at the airport. Read below for travel tips concerning weighing personal items and checked luggage.

Weight or Piece?

Checked baggage allowances can be defined in two different ways. The “piece concept” will be familiar to North American travelers, and refers to the number of bags each passenger can check in. Each bag has a maximum weight – typically 50 pounds – and a maximum permitted measurement of 62 inches.

Flights outside North America often use the alternative “weight concept,” in which passengers’ baggage allowance is expressed as a weight, usually accompanied by a permitted number of bags. Most often this is designated to ensure items will fit in the overhead bin, will not effect the weight of the aircraft itself and or to ensure passenger comfort.

International Flights

International airlines may have different specifications its passengers must follow. The absolute maximum weight for a single checked bag is fixed at 70 pounds by IATA. Airlines are unlikely to accept bags weighing above this maximum, as they are judged too heavy for staffers to lift. However, your specific airline may implement a lower allowance, or discriminate between ticket types. For example, Delta Airlines has a 50 pound-per-bag maximum for economy passengers, but a 70-pound maximum for passengers flying in business or first class.

This applies to all routes, both domestic and international, with the exception of flights to and from Brazil, where all passengers can pack up to 70 pounds in a single bag, regardless of the type of ticket they hold. Be sure to double check any size restrictions listed by the airline you are flying as well.

Domestic Flights

Allowances for domestic flights tend to be lower than those for international routes. For example, both WestJet and Southwest Airlines have a maximum baggage weight of 50 pounds, although it's possible to carry heavier bags for an additional fee. Southwest offers a higher allowance for military passengers on active service or carrying a permanent change of station orders, who can pack up to 100 pounds into a single bag without any extra charge.

If you are traveling United Airlines, Spirit Airlines, American Airlines or any other major airline that travels domestically, most of these rules will still apply.

Carry-On Baggage

Many U.S. airlines don’t impose any weight restrictions on carry-on baggage, but there are exceptions, so be sure to check before you travel to the airport. Even if an airline doesn’t have any weight restrictions, bear in mind that you'll have to lift your bag into the overhead locker, so don’t pack anything heavier than you can lift. Don’t forget that carry-on baggage will be subject to TSA security screening, so don’t pack liquids, gels or anything dangerous. Check the TSA website for the latest information on what’s permitted to travel in the airplane cabin.

Carry on items are most often laptop bags, duffel bags or backpacks, but carrying a pet onto a flight (if allowed) often counts as a carry on item as well. Animals add another layer to bringing a a carry on. First ensure that the airline will allow a pet to fly, but then be sure to check what the size limits and weight allowance of an animal carrier are for a flight.