What does BAC mean?

If you’ve done any research on DWI you’ve seen the term BAC, and may be wondering what that means. Blood alcohol concentration is the abbreviation for “blood alcohol content”. The phrase actually used in the penal code is “alcohol concentration”. That phrase is defined as the number of grams of alcohol in:

  • 210 liters of breath
  • 100 milliliters of blood, or
  • 67 milliliters of urine

This is important because “intoxicated” means having an alcohol concentration of .08 or more.

When you put all that together, you can commit the offense of driving while intoxicated when you operate a vehicle with an alcohol concentration of .08 or more.

You might wonder why lawyers refer to BAC when a breath test is taken. If BAC means blood alcohol content, that should apply only to blood tests right? Technically, you would be right. However, there is a reason for it – other than “AC” doesn’t sound as good. The explanation is that breath tests are designed to measure the amount of alcohol in the blood. The alcohol in the blood is transferred in the lungs, and expelled , which is what breath tests are based on. The breath test machine makes the calculations, and prints out the number – which looks the same as a blood test.

If you’re paying attention you probably figured out that they don’t take 100 milliliters of blood, nor does the breathalyzer collect 210 liters of breath.  The result reported is based on a calculation to get that result from a much smaller sample. 100 milliliters is a little over 3 ounces; the actual amount in collected in a blood tube is generally 2-3 milliliters, so they have to perform a calculation to determine how much would be in 100 milliter. The same goes from 210 liters of breath - it be roughly the amount of air in a 55 gallon fish tank.

There are a lot of issues with blood tests and breath tests, but we won’t go there now.

Just because the reading from the breathalyzer or the blood test is over .08 doesn’t mean you are guilty. The State has to prove that reading is accurate, which is also another discussion.

If you’ve been arrested for drunk driving and want to talk with an experienced, board certified lawyer, give us a call at 254-296-0020.

Walter Reaves
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Criminal Defense Attorney Walter Reaves has been practicing law for over 30 years.