Blood Alcohol Concentration (BAC) is a measurement of the amount of alcohol present in a person's bloodstream. It is usually expressed as a percentage, indicating how much alcohol is in a given volume of blood. For example, a BAC of 0.08% means that there are 0.08 grams of alcohol for every 100 milliliters of blood. BAC is commonly used to assess a person's level of intoxication, especially in relation to driving. Different factors, such as body weight, gender, and the rate of alcohol consumption, can influence an individual's BAC. Legal limits for driving vary by location, but many places set the limit at 0.08%.