Can I put 3.4oz (100ml) of liquid in a larger bottle, when traveling in the US?
Is the restriction on the amount of liquid in the container, or the size of the container itself?
The 3-1-1 page says:
Liquids, gels, aerosols, creams and pastes must be 3.4 ounces (100ml) or less per container
It sounds like it's on the amount of liquid, rather than the container itself.
I ask because I have a nice 4oz Nalgene travel container. What if I filled it half way up? That way, it's clearly less than 3oz, probably closer to 2oz.
While mathematically, your logic is sound, the answer is almost always no. Basically, they're not going to measure everything out. 3.4oz (or 100ml for simpler numbers) - what if you have 98ml or 95ml? They don't have the time or the inclination to measure all to say 'yes you're under 100ml'. As a result, it'll be on the bottle size.
Source: personal experience, when they've confiscated multiple almost-empty bottles from me :(
Liquids, gels, and aerosols must be in containers that are 3.4 ounces (100 ml) or smaller. Note that larger, half-full containers are not allowed.
Note, the container itself must be 3 oz. or less; a 4 oz. container that is half-full will not be allowed through the security checkpoint.
Note that if you have a bottle of (e.g.) cologne with 100ml written on it, it generally means it can fit a bit more than 100ml but it is sold with 100ml of perfume in it. No one at TSA will likely know that detail, though, so if the bottle says 100ml you are basically safe with it.
(This suggests an interesting hack: take a 4oz bottle, print a custom label identical to the original one but saying "3.4oz", and stick it on.)