Many people follow the "one drink an hour rule" to avoid going over the blood alcohol content of 0.08%. Essentially, the one drink per hour rule means that as long as someone only consumes 1¼ ounces of hard liquor, one beer, or one glass of wine and no more over the course of an hour, then they are safe to drive.
To calculate BAC, the amount of alcohol in the bloodstream is measured in milligrams (mg) of alcohol per 100 milliliters (ml) of blood. It is usually expressed as a decimal such as 0.08 or 0.15. For example, a BAC of 0.10% means that an individual's blood supply contains one part alcohol for every 1,000 parts blood.