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 100 milliliters of blood. For example, a BAC of 0.08% means 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 countries have legal limits for BAC while operating a vehicle, often set at 0.08% for adults. Higher BAC levels can impair judgment, coordination, and reaction times.