What's acceptable to bring on an airplane?

Specifically, I have a small bottle of lotion. On the bottle, it says there's 4.0 fl. ounces in it (when it's brand new, but I've been using it for a while so I know there's actually less in there). I know that you can only bring liquids on a plane up to 3.4 fl. ounces. So, would there be a problem if the bottle says 4.0 but there's 3.4 or less in there?