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.[1]
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 mL of blood.[1][2] In different countries, the maximum permitted BAC when driving ranges from the limit of detection (zero tolerance) to 0.08%.[3][2] BAC levels above 0.40% are potentially fatal.[1]
Units of measurement
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BAC is generally defined as a fraction of weight of alcohol per volume of blood, with an SI coherent derived unit of kg/m3 or equivalently grams per liter (g/L). Countries differ in how this quantity is normally expressed. Common formats are listed in the table below. For example, the US and many international publications present BAC as a percentage, such as 0.05%. This would be interpreted as 0.05 grams per deciliter of blood. This same concentration could be expressed as 0.5‰ or 50 mg% in other countries.[4]