Bloo alcohol content (BAC) or blood alcohol concentration is the concentration of alcohol in blood. It is usually measured as mass per volume. For example, a BAC of 0.02% means 0.2 ‰ (permille) or 0.02 grams of alcohol per 100 grams of individual's blood, or 0.2 grams of alcohol per 1000 grams of blood. Blood alcohol concentration is measured in many different units and in many different fashions, but they are all relatively synonymous for each other.