State blood-alcohol limits

The amount of alcohol in a person's body is measured by the weight of the alcohol in a certain volume of blood. This is called the blood alcohol concentration, or "BAC." Because the volume of blood varies with the size of a person, BAC establishes an objective measure to determine levels of impairment.

The measurement is based on grams per deciliter (g/dl), and in most states a person is considered legally intoxicated if his or her BAC is .08 g/dl or greater; that is, alcohol makes up one-tenth of one percent of the person's blood.