The legal blood alcohol limit in California is 0.08% for adults over 21, which means any more than that can result in a DUI charge. But the rules are a little different if you're underage.
For those of legal drinking age, 0.08% is estimated to be the equivalent of two drinks over the course of an evening. Still, to avoid being pulled over, it may be best to limit yourself to one drink or just stick to water.
And what about the under 21 crowd? Is it that younger people's metabolisms don't process alcohol as quickly? Nope, California's zero-tolerance law has nothing to do with intoxication.