Something I read in another thread just now made me wonder - why, in every other country (at least the ones I've been to) are you allowed 100 ml of liquids, but only 3 ounces in the US? Has anyone had luck traveling with 100 ml liquid containers in the US?

And please, "Because the TSA can't do math" isn't an answer. There must be some sort of explanation, right?

Because the US uses imperial measurements and the rest of the world uses metric? 100 ml is just over 3 ounces.

Exactly....so why do we get stuck being able to carry less? Shouldn't we be allowed to carry 3.4 oz?

The published TSA rule is 3.4 ounces, however they use their cutesy 3-1-1 campaign to try and get the public to remember their inane rules.

I find it very rare that TSOs are paying that close attention anyway. I used to regularly travel with toiletry products in bottles around 4 or 4.5 oz. because one product I used didn't come in anything smaller, and they never blinked an eye as long as they were in the quart bag. Even before I had PreCheck I eventually stopped taking out my 3-1-1 bag unless asked, which was maybe once every 15 flights.

TSA will let you bring up to 100ml, which is ~3.4 oz. Agree it's rare to be asked to take the 3-1-1 baggie out of your bag (though not doing so gives them an instant "bag check!" excuse if they so desire). It's also rare they notice liquids up to about 4 oz or so that happen to be in the 3-1-1 bag.

Remember, too, that liquids over 100ml can be brought if they're medically necessary.

Have you ever actually been denied the ability to carry any liquid between 3.0 and 3.4 oz?

I have a few bottles that actually say 100 ml and have never had a problem.

I haven't taken my bag our in a while either. I was just curious if they'd confiscate bottles that were 3.4 oz and why.

They won't. The limit is 100ml (3.4oz). It's often approximated as 3 oz on some signage.

The TSA explanation is here
http://blog.tsa.gov/2009/02/3-oz-or-...hat-gives.html

Some of the many previous threads about it

http://www.flyertalk.com/forum/pract...3-4-100ml.html

or

http://www.flyertalk.com/forum/pract...-gels-etc.html

or

http://www.flyertalk.com/forum/pract...rough-tsa.html

or

http://www.flyertalk.com/forum/pract...eckpoints.html

or

http://www.flyertalk.com/forum/pract...-oz-100ml.html

Cordelli has replied while I've been looking up links...

In the very early days, the US said "3 ounces" and the rest of the world said "100 ml" which of course are different. Within a few days or weeks, the TSA changed their rule to "3.4 oz" which is (nearly) 100 ml, and officially that's what you're allowed. However, the signs had been printed and the PA announcements recorded to say "3 ounces." Over at the PV (the TSA blog) and here on FT, many people asked why the signs and announcements couldn't be updated, and the consistent answer from TSA (as formalised in this link given by Cordelli) was "it's too hard, it's too expensive, and besides, you all know we really mean 3.4." (Note that the distinction between fluid ounces and ounces avoirdupois was also too hard, so they ignored it.)

One TSA person who posted here tried to argue that the "real" rule was 3 ounces but they had latitude to allow you up to 3.4 ounces. No, I never believed that either.

Officially the rule in the US is 3.4 ounces and it's on their website here. There have, however, been reports of individual screeners who claimed that the rule was 3 ounces, and who confiscated unilaterally allowed the passenger to voluntarily surrender a 3.2 or 3.3 ounce liquid. There was even one story of a screener who claimed that a container labeled 3.0 ounces was not allowed because "3.0 is more than just 3" Or this thread, where a 0.25 ounce bottle was confiscated because the screener thought it was 25 ounces.

As with everything else to do with the TSA, if you run into a screener who claims that 3 is the limit and tries to confiscate a 3.2 ounce container, you can try to show them a printout of the website but you'll likely be told that it's out of date or "we don't do it that way here" or "anyone could edit a website printout."

So, tragically, "the TSA can't do math" is one of the genuine answers.

As said, it was about a week after the introduction of the Freedom Baggie that the US realized that, not only were Europeans getting hosed, but that lots of products in the US are sized primarily in metric.

The US does not use imperial measurements.

Doesn't seem to matter as I get through security weekly with more than one baggie of liquids, and in many cases, bottles larger than 100ml.

Correct IIRC the USA uses
United States Customary Units.
(Our gallons are different, we don't use "stones" for weight, etc.)