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Blood Alcohol Concentration (BAC)

What is blood alcohol concentration (BAC)?

Blood alcohol concentration or blood alcohol content is the amount of alcohol in a certain volume of blood.

Chart 1. Blood Alcohol Concentration (BAC) Units
PLACE	UNITS	0.1 g alcohol in 100 mL blood equals:
U.S., Canada, Australia	percent (grams alcohol per 100 milliliters blood)	0.1%
UK	mg% (milligrams alcohol per 100 milliliters blood)	100 mg%
Europe (certain countries)	permille (grams alcohol per 1 liter blood)	1‰
Internationally, in hospitals	millimols alcohol per liter blood	22 mmol/L

Chart 1 source: ^[2]

What can influence the blood alcohol concentration (BAC)?

Your body weight. If your body weight is 100 lbs (45 kg) and you drink four glasses of 12% wine within one hour, your BAC may reach 0.15 g/100 mL, and if your weight is 240 lbs (109 kg), your BAC may reach only 0.06 g/100 mL ^[1]. This is because heavier individuals have more tissue in which alcohol can be diluted, so less alcohol will remain in their blood.
Your body fat. From the persons of the same body weight, those with a higher fat percent will have higher BAC after drinking the same amount of alcohol, because alcohol is poorly soluble in fat, so more alcohol will remain in their blood ^[3]. In the persons with large amount of lean body mass a lot of alcohol can be dissolved in their muscles, so less alcohol will stay in their blood and they will therefore not become easily drunk – these persons are said to have “hollow legs”.
Your sex. In average, women have higher BAC (up to 30%) after consuming the same amount of alcohol in the same time as the men of the same weight ^[1]. This is because women in average have higher percent of body fat.
Individual differences in the rate of alcohol absorption. In one 1995 study, 97 regular male drinkers have drunk 0.51 g alcohol/kg body weight (which roughly equals to 200-450 mL of 12% wine) on an empty stomach within 10 minutes and their breath alcohol concentrations (BrAC) have peaked within 10 to 91 minutes after starting drinking ^[4].

Factors That Stimulate Alcohol Absorption and Thus INCREASE BAC

The greater the amount of alcohol you consume in a given time, the higher BAC you will reach. For example, if you a man and weigh 160 lbs (73 kg) and you drink four standard drinks (such as 600 mL or 20 oz of 12% wine) on an empty stomach within one hour, your BAC may reach 0.09, but when you drink the same amount within 4 hours (1 drink per hour), your BAC may reach only 0.02, because alcohol will be absorbed and eliminated from your body at about the same rate (1 drink per hour, which is about 0.015 g/100 mL/hour) ^[1].
Carbonated beverages and mixers (sparkling wine, soda) may stimulate gastric emptying and thus alcohol absorption ^[3,5]. In one study, vodka diluted with a carbonated mixer was absorbed 25% faster in average than vodka with a still mixer in most participants, but in few of them it was absorbed slower ^[6].

How long does alcohol stay in your system?

When you are arrested for driving under the influence (DUI) in the United States, you will be released when your blood alcohol concentration falls to 0.00 or 0.02 g/100 mL of blood (depending on the state).

Chart 2. Time to Reach 0.02 or 0.00 BAC (assuming your alcohol elimination rate is 0.015 g/100 mL/hour)
BAC	Time to reach 0.02 BAC	Time to reach 0.00 BAC
0.30	18 h 40 min	20 h
0.29	18 h	19 h 20 min
0.28	17 h 20 min	18 h 40 min
0.27	16 h 40 min	18 h
0.26	16 h	17 h 20 min
0.25	15 h 20 min	16 h 40 min
0.24	14 h 40 min	16 h
0.23	14 h	15 h 20 min
0.22	13 h 20 min	14 h 40 min
0.21	12 h 40 min	14 h
0.20	12 h	13 h 20 min
0.19	11 h 20 min	12 h 40 min
0.18	10 h 40 min	12 h
0.17	10 h	11 h 20 min
0.16	9 h 20 min	10 h 40 min
0.15	8 h 40 min	10 h
0.14	8 h	9 h 20 min
0.13	7 h 20 min	8 h 40 min
0.12	6 h 40 min	8 h
0.11	6 h	7 h 20 min
0.10	5 h 20 min	6 h 40 min
0.09	4 h 40 min	6 h
0.08	4 h	5 h 20 min
0.07	3 h 20 min	4 h 40 min
0.06	2 h 40 min	4 h
0.05	2 h	3 h 20 min
0.04	1 h 20 min	2 h 40 min
0.03	40 min	2 h
0.02	/	1 h 20 min
0.01	/	40 min

Alcohol Problems in Intimate Relationships: Identification and Intervention National Institute on Alcohol Abuse and Alcoholism
The University of North Carolina at Chapel Hill
Begleiter H, 1996, The Pharmacology of Alcohol and Alcohol Dependence
Friel PN et al, 1995, Variability of ethanol absorption and breath concentrations during a large-scale alcohol administration study PubMed
Holt S et al, 1981, Observations on the relation between alcohol absorption and the rate of gastric emptying PubMed Central
Roberts C et al, 2007, Alcohol concentration and carbonation of drinks: the effect on blood alcohol levels PubMed