Free BAC Calculator – Measure Blood Alcohol Concentration & Sober Up Time

This blood alcohol concentration BAC calculator determines both blood alcohol content and how long alcohol stays in your system.

It is the ethanol’s weight (Ethyl alcohol) in a volume of blood or breath. In the United States, the standard measure is “grams of ethanol in 100 milliliters of blood” or 210 liters of breath. BAC is a percentage such as 0.10 or 0.245. Thus, it is blood alcohol content and blood alcohol level.

This unit quickly computes what it might be at the end of a drinking session. It also estimates the time it could take to metabolize that level to zero. The answers should not be taken as absolute, as every person is different.

Click on the graphic image icon and fill in these questions:

  • Gender
  • Weight
  • Number of Drinks
  • Hours Spent Drinking

Then click the “calculate” button, and that’s it, fast and easy. The results will display as the estimate at the end of drinking, and the approximate time it might go down to 0.0000.


The formula used is a procedure provided courtesy of Herbert Moskowitz, Ph.D., a noted alcohol researcher. These calculations are the National Safety Board, Department of Transportation’s formulation.

Once it is computed based on the above variables, the percentage of alcohol metabolized during drinking time is subtracted. (note: this formula uses what is considered a conservative basis of .012 per hour decline in the body’s alcohol level).

There are other aspects; age, tolerance, and physical fitness. These variabilities could produce a small fraction of error in the final answer. Here is how they might affect the outcome of our formulation.

Age: Younger people have a higher proportion of body water as a fraction of their total weight, and older people have less. So, a younger person may potentially have a lower rate than an older person.

Physical Fitness: Individuals who may be overweight may have a smaller proportion of their body weight than water. Lean people tend to have a more significant fraction of their body weight than water. Therefore, overweight people could have a lower than our formula indicates.

Tolerance: A regular drinker will have a higher ability to metabolize alcohol than someone who is not.

Even a tiny amount of alcohol can impair the judgment, timing, and coordination of someone’s ability to operate a motor vehicle.

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