The Transportation Security Administration and airlines place restrictions on the size of luggage and some of the items contained within for safety and comfort reasons. The TSA forbids items deemed dangerous on board planes, while airlines limit the amount and size of carry-on luggage to increase comfort in the passenger compartment. Even checked luggage is limited in size and scope.

Carry-On Luggage Sizes

Airlines put limits on the size of luggage you can bring on board the plane as well as the number of items allowed to keep the interior safe and uncluttered. The actual dimensions allowed by airlines vary to minor degrees, but generally the luggage must fit below the seat in front of you or in the overhead compartments. If your bag is no more than 22 inches tall, 14 inches wide and 9 inches deep, you will usually be allowed to bring it on board. Most airlines have racks in which you can place your bag at their service counters for testing purposes. If your luggage fits, you can bring it on board.

Liquid Allowances

The TSA has created a handy numeric device to help travelers remember the carry-on rule for liquids. It's, simply, 3-1-1. You can carry on liquids, gels or aerosols 3.4-ounces or less. These items should be placed in one quart-sized clear plastic bag, and only one bag is allowed per passenger. The bag should be placed in a screening bin outside of the rest of your luggage for quicker security clearance. Some exceptions apply. You can bring larger quantities of essential liquids, such as breast milk, baby formula and medications. You must declare these at the checkpoint, and the TSA asks that you only bring on board what you need for the flight.

Checked Luggage and Fees

Most airlines have implemented fees they charge if you checked more than one bag, while some make customers pay a fee for the first checked bag. You will usually pay a fee if your bag weighs more than 50 pounds and will also be charged extra for oversizes items such as skis and snowboards. The general size allowance for checked luggage is a total of 62 linear inches (the length plus width plus height), such as 27-by-21-by-14 inches.

Oversized Items

You can check large, bulkier items such as skis on many flights, but expect to pay an extra fee. Airlines usually consider an item oversized if it has total dimensions beyond 62 linear inches. You can bring nondangerous fragile items, such as paintings, on many airplanes, but you must buy an extra ticket. Generally, your onboard item shouldn't exceed 100 pounds and can't block access to emergency exits or cabin aisles.