It depends on alot of factors. Your weight, how fast your metabolism is, how many drinks you've had. Generally I'd say unless you drunk a truck load of beer, you'll come up clean after 24 hours. One beer or an ounce of alcohol usually leaves your system between one and 2 hours. I've heard that anything less than 24 hours you'll come up dirty, but I once drank 2 bottles of wine to my head and tested clean on a court appointed test only 14 hours later. Hope this helps.