Liquids and gels are usually labeled in fluid ounces. Nobody buys two pound of milk; they buy a quart of milk.
Ahhh.....but toothpaste is measured in ounces by weight. I can fit 4 weight ounces of toothpaste into a 1 fluid (volume) ounce container. I know that they aren't weighing items and that they are truly going by volume but they need to say "3 fluid ounce" container if that's what they mean. Or can I bring a 3 ounce (by weight) tube of toothpaste even if it's bigger than a 3 fluid ounce container?