The Widmark Formula and Calculating Your BAC Level

Calculate Your BAC I’ve written previous articles on alcohol consumption and absorption as it relates to a person’s Blood Alcohol Content (BAC) in drunk driving cases. Most people have no idea how much alcohol it takes to go over the legal limit in Pennsylvania (.08 BAC).  While some wrongly believe that they can estimate their level of intoxication based on the way they feel after drinking, a built up tolerance may provide someone with a false belief or confidence that they aren’t legally drunk.

Remember that while each of us has a different tolerance level based on our own alcohol consumption habits, we all expel (metabolize) alcohol from our bodies at the same rate–.015% per hour.  This rate is the same for everyone regardless of body type, weight, height or what you drank (liquor, wine, beer) or the food that you consume (i.e. “eat some bread it will soak up the alcohol or drink some coffee to sober up.)

You can, however, roughly calculate your BAC without any devices with a mathematical equation known as the Widmark Formula.  The equation is named for a Swedish Scientist, Erik M.P. Widmark (1889-1954) who was considered a pioneer in the field of forensic toxicology.  His major contribution to this field was addressing alcohol’s absorption, distribution and elimination in people.   These issue deal directly with concept of retrograde extrapolation which is using a person’s BAC level at a known time (the time of the breath or blood test) to estimate their BAC at earlier point of time (time of driving) driving under the influence (DUI) cases.

The Widmark formula calculates a person’s BAC with the following information:

  • Weight
  • Gender
  • Amount of Alcohol consumed in a given period


The formula is as follows:

BAC = [Alcohol consumed in grams / (Body weight in grams x R)] X 100


The factors in this equation are defined as follows:

  • R = Gender – a constant in this equation (.55 for females and .68 for males)
  • Grams of Alcohol Consumed (Number of drinks x 14)
    • To calculate this amount, you need to make the assumption that you are drinking “standard” sized drinks
    • The standard sized drinks are as follows:
      • 80 proof version of liquor (i.e. gin or whiskey) – 1.5 ounces
      • Beer (5.0% alcohol) – 12 ounces
      • Wine (12.0 alcohol) – 5 ounces
    • In the United States, the standard sized drink continues 14 grams of alcohol
  • Body weight in grams
    • Body weight in pounds x 454 = bodyweight in grams


A 180 lb male who has drank 4 beers over the course of 2 hours will have the following BAC level.

4 beers x 14/ [(180×454) x .68)] x 100 =

56 / [55,570] x 100 = .10 BAC (above the PA legal limit of .08)

This, however, may not be an accurate BAC!



You must keep in mind that everyone metabolizes alcohol at the same rate–.015 an hour.   You must therefore include this factor in the above equation.   If our 180 lb male had been drinking for 2 hours, his BAC would be .10 -.030 = .07 BAC   (below the legal limit)



The Widmark calculation is fairly simple even for person like me who was never did that well in math. For more information on drunk driving charges, visit my free resource section or watch my videos.