In order to understand just how much you can have to drink before you reach the legal intoxication level, you must realize that not all drinks are equal. A bottle of beer, for instance, is not the same as a tumbler glass of vodka on the rocks. Twelve ounces of beer is the equivalent of five ounces of wine or just 1.5 ounces of liquor.
Consider a male (200 pounds) and female (150 pounds) going out for a few drinks. If she has four small glasses of wine and he has four beers, she will have a BAC of .135 and he would also be beyond the legal limit at .087 BAC.
So, legally, the man might be able to drive after three drinks, but remember that even at much lower BAC, driving can be impaired. At .05 BAC, a person will demonstrate exaggerated emotions, a decrease in reaction time and impaired judgment. That man would easily reach this level after his third drink.
It is also important to understand that it takes a long time for a person to burn off the alcohol in his or her system. For each hour that passes, the body’s BAC drops by .015. In other words that woman, having had four drinks, could not legally drive for more than three hours after her last drink (.015 * 3 = .045; .135 -.045= .09). Worse yet, there are often people still drunk while driving to the office in the morning. A person that goes out and binge drinks in the evening, sleeps a few hours, and then makes the commute to work can easily still fall beyond the legal level of intoxication when reaching the office.