It's a 'how long is a piece of string' argument because there are so many variables - how old are you, how heavy are you, when did you last eat, when did you last drink alcohol, how much do you regulalry drink, and so on. All these variables have an effect on the amount of alcohol you absorb at any one time. For insatnce, I am teetotal, so one pint of 5.2% would ensure I was under the legal drink / drive limit, but incapable of driving safely. The short answer to the question is - if you want to drive, don't drink!