The Transportation Security Administration (TSA) states on their website (www.tsa.gov):

3-1-1 for carry-ons = 3 ounce bottle or less (by volume) ; 1 quart-sized, clear, plastic, zip-top bag; 1 bag per passenger placed in screening bin. One-quart bag per person limits the total liquid volume each traveler can bring. 3 oz. container size is a security measure.

Declare larger liquids. Medications, baby formula and food, and breast milk are allowed in reasonable quantities exceeding three ounces and are not required to be in the zip-top bag. Declare these items for inspection at the checkpoint.

*** UPDATE (10-27-08), from the TSA.gov Official Blog:

3 oz or 3.4 oz? What gives???

OK, here’s the scoop. If the U.S. would have switched to the metrics system in the 70s, this wouldn’t be an issue.

When the TSA lifted the total liquid ban and implemented the 3-1-1 program, the permissible amount of liquids, aerosols and gels was 3oz. Press releases went out, WebPages were updated, and signs were printed and shipped out nationwide to 457 airports. A lot of work went into the 3-1-1 campaign.

When the TSA rolled this out, the European Union was not on board yet. When the EU decided to allow liquids to travel, the amount permitted was 100ml. Well, as we all know, 100ml = 3.4oz. not 3 oz.

In order to align with the EU, we decided to allow liquids in containers up to 3.4oz, but we decided to keep our signage the same. The 3-1-1 program was so successful, that it would have been a shame to change it to 3.4-1-1. J

TSOs nationwide should be allowing liquids up to 3.4oz. If they are not, you can ask for a supervisor or you can use our Got Feedback program.