What is BAC and How is it Calculated?

The term BAC is most often associated with a Driving While Intoxicated arrest and stands for Blood Alcohol Concentration. A BAC is represented as a percentage after a test of a person’s blood, breath, or urine. For example, a BAC of 0.10 percent means that there is one gram of alcohol for every 1000 grams of a person’s blood. In most states, a driver is considered “legally intoxicated” when their BAC is at or above 0.08 grams.

For the majority of law enforcement agencies, the most common test used to determine a driver’s BAC is a breath test which many refer to a “breathalyzer”. It is thought that there is a direct correlation between the amount of alcohol found in a subject’s deep lung air and the amount of alcohol in their blood. The results of a breath alcohol test are sometimes known as a BrAC. Breath tests are a favorite of law enforcement because they are conducted by the officers themselves and they offer immediate results as opposed a blood or urine test which can take weeks or months to return. Breathalyzers are generally not as accurate as a blood test but are more accurate than urine.

A BAC cannot always be simply determined by the number of drinks that a person has consumed and is not a specific measure of impairment. Roughly, a single drink containing one ounce of alcohol will increase a person’s BAC by approximately 0.03 grams. However, a person’s body chemistry, size, gender, and tolerance are all major factors that can affect a BAC and level of impairment.

In reference to driving, law enforcement is forced to set a standard at which a person is considered impaired in order to meet their objectives. When a driver’s BAC has reached 0.08 grams, they are automatically considered to be DWI whether they are impaired or not.