The University of Oklahoma Police Department has created a website to help determine your blood alcohol content. The website uses averages to create theoretical data. For example, a 120 pound person that drinks three champagne glasses, five ounces each, in one hours time would have a BAC level of .09%. That's above the legal limit in all states.
The calculator and charts are based on averages, and are not to be used to determine a level of impairment if you plan to drive.
The website can be found here: BAC Calculator