Figuring what to bring in a carry-on bag can be stressful. Travelers don't always realize the exact rules for carry-on luggage when flying, although there's an easy way to help remember what to do when it comes to liquids.

The Transportation Security Administration, or TSA, sets and enforces the rules for air travel in the United States and its 3-1-1 rule limits the amount of liquids and gels a passenger can bring on an airplane. Knowing the 3-1-1 rule and other travel tips will help you pack successfully for your trip, stress-free.

The 3-1-1 Liquids Rule

The TSA’s 3-1-1 rule limits the amount of liquid you can bring on an airplane in your carry-on luggage. It does not apply to checked bags, as they go through a separate additional screening and x-rays.

  • Passengers are limited to using plastic bags or other containers no larger than 3.4 oz. for their liquids.
  • All containers of liquid which must be placed in a 1 qt., transparent, plastic, sealable bag. Each passenger may have only one bag for liquids.
  • Passengers can bring on as many 3.4-oz. containers as they can fit in the quart-sized bag when it is sealed.

The TSA’s 3-1-1 liquids rule can limit the kinds of toiletry bags you bring and means you may need to get travel-sized toiletries to bring, like lotions, toothpastes, hand sanitizers, face creams, and smaller makeup like mascaras or concealers. The TSA liquids rule also means you can’t have water in your water bottle or the security officers will have to discard your bottle since it is larger than a 3.4-ounce container.

Specific Exceptions

The TSA allows a very limited number of exceptions to the 3-1-1 rule. Passengers can pack necessary liquids and pastes in their carry-on bags medicine, baby food and formula, breast milk, liquids such as water or orange juice for passengers with a special condition and frozen items--even if the item exceeds the 3-1-1 limits.

The TSA says passengers should carry on only what will be needed during the flight but does not place a specific volume limit, saying only that these exceptions are allowed in "reasonable quantities."

The 3-1-1 rule does not apply to toiletries you have packed in your checked luggage.

Security Procedures

When you go through airport security checkpoints, you must take out your quart-sized bag of liquids and place it separately into a security bin for security screening at the TSA checkpoint.

If you have liquids that are exempt from the 3-1-1 requirements, you must declare them to the TSA officer at the checkpoint, and they may be subject to more thorough screenings, so prepare extra time for this potential hassle during the screening process.

About the Rule

On Aug. 10, 2006, authorities in the United Kingdom arrested a group suspected of planning to blow up a large number of airplanes using a sports drink and other chemicals to make an explosive cocktail.

In the aftermath, the TSA banned all liquids in carry-on baggage in flights leaving from or coming to the US. After rigorously testing liquids, the TSA implemented the 3-1-1 rule in September 2006.

Other Countries

The 3-1-1 rule is used in many countries around the world, including members of the European Union, Canada, Mexico, China, South Korea, New Zealand and Australia.

After the US and Canada implemented the 3-1-1 rule, the European Union, Norway, Switzerland and Iceland adopted the 3-1-1 rule so that transportation safety rules would be more uniformly administered around the world.

The TSA also protects American travelers by conducting inspections of air carriers who fly to the US, ensuring that foreign airports conform to TSA standards, offering training for foreign airline employees and making sure international security standards are being enforced.