Blood alcohol content (BAC), also called blood alcohol concentration or blood alcohol level, is a measurement of alcohol intoxication used for legal or medical purposes. 
BAC is expressed as mass of alcohol per volume of blood. In the US and many international publications, BAC levels are written as a percentage such as 0.08%, meaning that there is 0.08 g of alcohol for every 100  of blood. In different countries, the maximum permitted BAC when driving ranges from the limit of detection (zero tolerance) to 0.08%. BAC levels above 0.40% are potentially fatal.