The background to this calculator and the formulas used to calculate BAC are from Chapter 10,
 Alcohol and Traffic Safety of Traffic Safety

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 *The estimates are based on drinks containing 0.5 fluidounces (15 mL) of alcohol, close to a typical serving of beer, wine, or spirits.  The same amount of alcohol consumed in the same time produces approximately the same BAC, regardless of the type of drink.  About 0.5 fluidounces of alcohol is contained in a typical serving of beer (12 fluidounces), of wine (4 fluidounces,) or scotch (1.3 fluidounces -- although a common measure is 1.5  fluidounces) or other similar strength liquor.

These are  typical estimates.  The BAC reached by an individual may vary for many reasons, including food consumption.  The performance and behavior changes at a given BAC vary substantially between individuals.  This calculation is a guide based on average responses.  There is no guarantee that you will be measured to be within legal limits even if the calculation indicates that you are marginally legal.

Blood Alcohol Concentration (BAC) is the percent, by weight, of alcohol in the blood.  It is illegal to drive with a BAC exceeding an amount specified in law.  Legal limits vary - from 0.02% in Sweden to 0.08% in all  US states (as of November 2005).