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; it is expressed as mass of alcohol per volume or mass of blood. For example, a BAC of 0.10 by (0.10% or one tenth of one percent) means that there is 0.10 g of alcohol for every 100  of blood, which is the same as 21.7 . A BAC of 0.10 by (0.10%) is 0.10 g of alcohol per 100 g of blood (23 mmol/L). A BAC of 0.0 is sober; in different countries the maximum permitted BAC when driving ranges from about 0.02% to 0.08%; BAC levels over 0.08% are considered impaired; above 0.40% is potentially fatal.
