The blood alcohol concentration (BAC) is a measure of the quantity of alcohol present in a person's blood stream. Usually, social drinkers do not exceed BAC levels of 0.1. Keep in mind, at BAC levels of 0.08, it is illegal for a person to drive.
At BAC levels above 0.1, high levels of judgement and motor skill impairment occur, with blackouts occurring at BAC levels of 0.2.