Blood Alcohol Concentration (BAC) is used legally as well as medically to gauge the level of intoxication in a person who has consumed alcohol. Even though two people may consume the same number of alcoholic drinks, their blood alcohol concentrations at a given time will vary because alcoholism metabolism varies with gender and build. While it is expressed in terms of milligrams per deciliter (mg/dl) in India, in many parts of the world, it is expressed in grams per 100 milliliters (g/100ml). According to section 185 of the Motor Vehicles Act 1988 (amendment made in 1994), in India, 0.03% is the legal limit for the blood alcohol concentration, a value beyond which a person is not allowed to drive any motor vehicle.

BAC or the number of drinks consumed are not useful in assessing impairment in an individual as tolerance to alcohol varies from person to person depending upon his or her genes and habituation to alcoholism. While calculators give an estimate of the blood alcohol content, the exact value can be measured by testing the blood sample in a laboratory or by the use of breath analyzing equipment.