Results of a breath alcohol analysis are expressed in terms of weight-to-volume; weight of alcohol (expressed in grams) per volume of breath (210 liters). Results of a breath test are read as Breath Alcohol Concentration or BrAC, but are often interpreted as BAC.
For example, an alcohol concentration of 0.100 means that there are 0.100 grams of alcohol per 210 liters of breath, which equals 0.100 BrAC or 0.100 BAC.
