Blood alcohol content (BAC), also called blood alcohol concentration, blood ethanol concentration, or blood alcohol level is most commonly used as a metric of alcohol intoxication for legal or medical purposes. Blood Alcohol Content is the legal name for BAC but Blood Alcohol Concentration is sometimes used for simpler description.
Blood alcohol content is usually expressed as a percentage of alcohol (generally in the sense of ethanol) in the blood in units of mass of alcohol per volume of blood or mass of alcohol per mass of blood, depending on the country. For instance, in North America a BAC of 0.1 (0.1% or one tenth of one percent) means that there are 0.10 g of alcohol for every dL of blood.
To calculate estimated peak blood alcohol concentration (EBAC), a variation, including drinking period in hours, of the Widmark formula was used. The formula is:
where 0.806 is a constant for body water in the blood (mean 80.6%), SD is the number of standard drinks containing 10 grams of ethanol, 1.2 is a factor to convert the amount in grams to Swedish standards set by The Swedish National Institute of Public Health, BW is a body water constant (0.58 for men and 0.49 for women), Wt is body weight (kilogram), MR is the metabolism constant (0.017) and DP is the drinking period in hours. Regarding metabolism (MR) in the formula; Females demonstrated a higher average rate of elimination (mean, 0.017; range, 0.014-0.021 g/210 L) than males (mean, 0.015; range, 0.013-0.017 g/210 L). Female subjects on average had a higher percentage of body fat (mean, 26.0; range, 16.7-36.8%) than males (mean, 18.0; range, 10.2-25.3%). Additionally, men are, on average, heavier than women but it is not strictly accurate to say that the water content of a person alone is responsible for the dissolution of alcohol within the body, because alcohol does dissolve in fatty tissue as well. When it does, a certain amount of alcohol is temporarily taken out of the blood and briefly stored in the fat. For this reason, most calculations of alcohol to body mass simply use the weight of the individual, and not specifically his/her water content. Finally, it is speculated that the bubbles in sparkling wine may speed up alcohol intoxication by helping the alcohol to reach the bloodstream faster. A study conducted at the University of Surrey in the United Kingdom gave subjects equal amounts of flat and sparkling Champagne which contained the same levels of alcohol. After 5 minutes following consumption, the group that had the sparkling wine had 54 milligrams of alcohol in their blood while the group that had the same sparkling wine, only flat, had 39 milligrams.
80 kg male drinking 3 standard drinks in two hours:
70 kg woman drinking 2.5 standard drinks in two hours:
There are several different units in use around the world for defining blood alcohol concentration. Each is defined as either a mass of alcohol per volume of blood or a mass of alcohol per mass of blood (never a volume per volume). 1 milliliter of blood is approximately equivalent to 1.06 grams of blood. Because of this, units by volume are similar but not identical to units by mass. In the U.S. the concentration unit 1% w/v (percent mass/volume, equivalent to 10g/l or 1 g per 100 ml) is in use. This is not to be confused with the amount of alcohol measured on the breath, as with a breathalyzer. The amount of alcohol measured on the breath is generally accepted as proportional to the amount of alcohol present in the blood at a rate of 1:2100. Therefore, a breathalyzer measurement of 0.10 mg/L of breath alcohol converts to 0.0001×2100 g/10dL, or 0.021 g/dL of blood alcohol (the units of the BAC in the United States). While a variety of units (or sometimes lack thereof) is used throughout the world, many countries use the g/L unit, which do not create confusion as percentages do. Usual units are highlighted in the table below.
Map of Europe showing countries' blood alcohol limits as defined in g/dl for the general population.
For purposes of law enforcement, blood alcohol content is used to define intoxication and provides a rough measure of impairment. Although the degree of impairment may vary among individuals with the same blood alcohol content, it can be measured objectively and is therefore legally useful and difficult to contest in court. Most countries disallow operation of motor vehicles and heavy machinery above prescribed levels of blood alcohol content. Operation of boats and aircraft are also regulated.
The alcohol level at which a person is considered legally impaired varies by country. The list below gives limits by country. These are typically blood alcohol content limits for the operation of a vehicle.
Zero effective tolerance
It is illegal to have any measurable alcohol in the blood while driving in these countries. Most jurisdictions have a tolerance slightly higher than zero to account for false positives and naturally occurring alcohol in the body. Some of the following jurisdictions have a general prohibition of alcohol.
Croatia—professional drivers, driving instructors and drivers of the vehicle categories C1, C1+E, C, C+E, D, D+E and H; the limit for other drivers is 0.50 mg/g, but they do get an additional separate fine if they cause an accident while having a blood alcohol level between 0 and 0.50 mg/g 
Israel—24 mg per 100 ml (0.024%) of breath (penalties only apply above 26 mg per 100 ml (0.026%) of breath due to lawsuits about sensitivity of devices used). New drivers, drivers under 24 years of age and commercial drivers 5 mg per 100 ml of breath.(0,005%) 
Israel 24 mg per 100 ml (0.024%) of breath (penalties only apply above 26 mg per 100 ml (0.026%) of breath due to lawsuits about sensitivity of devices used). New drivers, drivers under 24 years of age and commercial drivers 5 mg per 100 ml of breath.(0,005%) 
Netherlands (for drivers in their first five years after gaining a driving license)
Norway (road vehicles and sea vessels over 15 m), alternatively 0.1 mg/L of breath.
Argentina (0.02% for motorbikes, 0.00% for truck, taxi, and bus drivers)
Australia (0.00% for Australian Capital Territory learner, provisional and convicted DUI drivers (changed down from 0.02% on December 1, 2010), 0.02% for truck/bus/taxi, 0.00% for learner drivers, provisional/probationary drivers (regardless of age), truck and bus drivers, driving instructors and DUI drivers in all other states)
Austria - no limit for pedestrians; 0.08% for cycling; 0.05% generally for cars <7,5 t (driving licence B) and motorbikes (A); but 0,01% during learning (for driver and teacher or L17-assistant), during probation period (at least the first 2 years) or up to the age of 20 (A1, AM, L17, F), trucks (C >7,5 t), bus (D), drivers of taxi and public transport 
Croatia—professional drivers, driving instructors and drivers of the vehicle categories C1, C1+E, C, C+E, D, D+E and H; the limit for other drivers is 0.50 mg/g, but they do get an additional separate fine if they cause an accident while having a blood alcohol level between 0 and 0,50 mg/g 
Germany (0.0‰ for learner drivers, all drivers 18–21 and newly licensed drivers of any age for first two years of licence; also, if the BAC exceeds 0.3‰, driving is illegal if the driver is showing changes in behavior ("Relative Fahruntüchtigkeit"))
Portugal (0.02% for drivers holding a driver's licence for less than three years, professional drivers, and drivers of taxis, heavy vehicles, emergency vehicles, public transport of children and carrying dangerous goods).
United States—all states impose penalties for driving with a BAC of 0.08% or greater. Even below those levels drivers can have civil liability and other criminal guilt (e.g., in Arizona driving impairment to any degree caused by alcohol consumption can be a civil or criminal offense in addition to other offenses at higher blood alcohol content levels). Drivers under 21 (the most common U.S. legal drinking age) are held to stricter standards under zero tolerance laws adopted in varying forms in all states: commonly 0.01% to 0.05%. See Alcohol laws of the United States by state. Federal Motor Carrier Safety Administration: 0.04% for drivers of a commercial vehicle requiring a commercial driver's license and 0.01% for operators of common carriers, such as buses.
Limits by country (BrAC: Breath Alcohol Content)
In certain countries, alcohol limits are determined by the Breath Alcohol Content (BrAC), not to be confused with blood alcohol content (BAC).
In Greece, the BrAC limit is 250 microgrammes of alcohol per litre of breath. The limit in blood is 0.50 g/l. The BrAC limit for drivers in their first two years after gaining a driving license and common carriers is 100 microgrammes per litre of breath.
BrAC 400–600 = €700 fine, plus suspension of driving license for 90 days (introduced in 2007)
BrAC >600 = 2 months imprisonment, plus suspension of driving license for 180 days, plus €1,200 fine
In Hong Kong, the BrAC limit is 220 microgrammes per litre of breath (as well as other defined limits)
In The Netherlands and Finland, the BrAC limit is 220 microgrammes of alcohol per litre of breath (μg/l, colloquially known as "Ugl").
In New Zealand, the BrAC limit is 250 micrograms of alcohol per litre of breath for those aged 20 years or over, and zero for those aged under 20 years.
In Singapore, the BrAC limit is 350 microgrammes of alcohol per litre of breath.
In Spain the BrAC limit is 250 microgrammes of alcohol per litre of breath and 150 microgrammes per litre of breath for drivers in their first two years after gaining a driving license and common carriers.
In the United Kingdom the BrAC limit is 350 microgrammes of alcohol per litre of breath (as well as the above defined blood alcohol content).
Other limitation schemes
For South Korea, the penalties for different blood alcohol content levels include
0.01–0.049 = No Penalty
0.05–0.09 = 100 days license suspension
>0.10 = Cancellation of car license.
"0.01" Blood alcohol content is the hundredth decimal part of the one thousandth part of a liter. (Please note that this "0.01" is measured in permille and not percentage as the "0.1" example in introduction and numbers in 1 Effects at different levels.)
One milliliter is one thousandth of a liter, therefore 1% of a milliliter (BAC 0.01) is 0.00001 L. For example, a blood-alcohol concentration of 0.08, denoting 0.08 mL/L, is equivalent to an absolute blood-alcohol volume of 0.00008 L within every liter of blood.
Each country or state may define BAC differently. For example, the state of California in the United States legally defines BAC as a ratio of grams of alcohol per 100 milliliters of blood, which is equal to grams of alcohol per deciliter of blood.
Since measurement must be accurate and inexpensive, several measurement techniques are used as proxies to approximate the true parts per million measure. Some of the most common are listed here: (1) Mass of alcohol per volume of exhaled breath (for example, 0.38 mg/L; see also breath gas analysis), (2) Mass per volume of blood in the body (for example, 0.08 g/dL), and (3) Mass of alcohol per mass of the body (for example, 0.0013 g/kg).
An ethanol level of 0.10% is equal to 22 mmol/l or 100 mg/dl of blood alcohol. This same 0.10% BAC also equates to 0.10 g/dL of blood alcohol or 0.10 g/210L of exhaled breath alcohol or 0.476 mg/L of exhaled breath alcohol. Likewise, 0.10 mg/L of exhaled breath alcohol converts to 0.02% BAC, 0.022 g/dL of blood alcohol or 0.022 g/210L of exhaled breath alcohol.
Blood alcohol tests assume the individual being tested is average in various ways. For example, on average the ratio of blood alcohol content to breath alcohol content (the partition ratio) is 2100 to 1. In other words, there are 2100 parts of alcohol in the blood for every part in the breath. However, the actual ratio in any given individual can vary from 1300:1 to 3100:1, or even more widely. This ratio varies not only from person to person, but within one person from moment to moment. Thus a person with a true blood alcohol level of .08% but a partition ratio of 1700:1 at the time of testing would have a .10 reading on a Breathalyzer calibrated for the average 2100:1 ratio.
A similar assumption is made in urinalysis. When urine is analyzed for alcohol, the assumption is that there are 1.3 parts of alcohol in the urine for every 1 part in the blood, even though the actual ratio can vary greatly.
Breath alcohol testing further assumes that the test is post-absorptive—that is, that the absorption of alcohol in the subject's body is complete. If the subject is still actively absorbing alcohol, their body has not reached a state of equilibrium where the concentration of alcohol is uniform throughout the body. Most forensic alcohol experts reject test results during this period as the amounts of alcohol in the breath will not accurately reflect a true concentration in the blood.
Auto-brewery syndrome is a rare medical condition where the stomach produces brewers yeast that breaks down starches into ethanol; which enters the blood stream.
Alcohol is absorbed throughout the gastrointestinal tract, but more slowly in the stomach than in the small or large intestine. For this reason, alcohol consumed with food is absorbed more slowly, because it spends a longer time in the stomach. Furthermore, alcohol dehydrogenase is present in the stomach lining. After absorption, the alcohol passes to the liver through the hepatic portal vein, where it undergoes a first pass of metabolism before entering the general bloodstream.
Alcohol is removed from the bloodstream by a combination of metabolism, excretion, and evaporation. The relative proportion disposed of in each way varies from person to person, but typically about 95% is metabolized by the liver. The remainder of the alcohol is eliminated through excretion in breath, urine, sweat, feces, milk and saliva. Excretion into urine typically begins after about 40 minutes, whereas metabolisation commences as soon as the alcohol is absorbed, and even before alcohol levels have risen in the brain.
Many physiologically active materials are removed from the bloodstream (whether by metabolism or excretion) at a rate proportional to the current concentration, so that they exhibit exponential decay with a characteristic halflife (see pharmacokinetics). This is not true for alcohol, however. Typical doses of alcohol actually saturate the enzymes' capacity, so that alcohol is removed from the bloodstream at an approximately constant rate. This rate varies considerably between individuals; Another sex based difference is in the elimination of alcohol. Persons below the age of 25, women and persons with liver disease may process alcohol more slowly. False High (BAC) readings are related to patients with proteinuria and hematuria, due to kidney-liver metabolism and failure (for example, Hematuria 1+ protenuria 1+ ) Such persons have impaired acetaldehyde dehydrogenase, which causes acetaldehyde levels to peak higher, producing more severe hangovers and other effects such as flushing and tachycardia. Conversely, members of certain ethnicities that traditionally did not use alcoholic beverages have lower levels of alcohol dehydrogenases and thus "sober up" very slowly, but reach lower aldehyde concentrations and have milder hangovers. Rate of detoxification of alcohol can also be slowed by certain drugs which interfere with the action of alcohol dehydrogenases, notably aspirin, furfural (which may be found in fusel alcohol), fumes of certain solvents, many heavy metals, and some pyrazole compounds. Also suspected of having this effect are cimetidine (Tagamet), ranitidine (Zantac), and acetaminophen (Tylenol) (paracetamol).
Currently, the only known substance that can increase the rate of metabolism of alcohol is fructose. The effect can vary significantly from person to person, but a 100g dose of fructose has been shown to increase alcohol metabolism by an average of 80%. Fructose also increases false positives of high BAC ratio readings in anyone with proteinuria and hematuria, due to kidney-liver metabolism.
Alcohol absorption can be slowed by ingesting alcohol on a full stomach. Spreading the total absorption of alcohol over a greater period of time decreases the maximum alcohol level, decreasing the hangover effect. Thus, drinking on a full stomach or drinking while ingesting drugs which slow the breakdown of ethanol into acetaldehyde will reduce the maximum blood levels of this substance and thus decrease the hangover.
Alcohol in carbonated beverages is absorbed faster than alcohol in non-carbonated drinks. Another study also confirmed this, conducted at the University of Surrey in the United Kingdom gave subjects equal amounts of flat and sparkling Champagne which contained the same levels of alcohol. After 5 minutes following consumption, the group that had the sparkling wine had 54 milligrams of alcohol in their blood while the group that had the same sparkling wine, only flat, had 39 milligrams.
Retrograde extrapolation is the mathematical process by which someone's blood alcohol concentration at the time of driving is estimated by projecting backwards from a later chemical test. This involves estimating the absorption and elimination of alcohol in the interim between driving and testing. The rate of elimination in the average person is commonly estimated at .015 to .020 grams per deciliter per hour (g/dl/h), although again this can vary from person to person and in a given person from one moment to another. Metabolism can be affected by numerous factors, including such things as body temperature, the type of alcoholic beverage consumed, and the amount and type of food consumed.
In an increasing number of states, laws have been enacted to facilitate this speculative task: the blood alcohol content at the time of driving is legally presumed to be the same as when later tested. There are usually time limits put on this presumption, commonly two or three hours, and the defendant is permitted to offer evidence to rebut this presumption.
Forward extrapolation can also be attempted. If the amount of alcohol consumed is known, along with such variables as the weight and sex of the subject and period and rate of consumption, the blood alcohol level can be estimated by extrapolating forward. Although subject to the same infirmities as retrograde extrapolation—guessing based upon averages and unknown variables—this can be relevant in estimating BAC when driving and/or corroborating or contradicting the results of a later chemical test.
Highest recorded blood alcohol level/content
There have been reported cases of blood alcohol content higher than 1.00%. In March 2009, a 45-year-old man was admitted to the hospital in Skierniewice, Poland, after being struck by a car. The blood test showed blood alcohol content at 1.23%. The man survived but did not remember either the accident or the circumstances of his alcohol consumption. One such case was reported by O'Neil, and others in 1984. They report on a 30-year-old man who survived a blood alcohol concentration of 1,500 mg/100 ml (1.5%) blood after vigorous medical intervention.
In South Africa, a man driving a Mercedes-Benz Vito light van containing 15 sheep, allegedly stolen from nearby farms, was arrested on December 22, 2010, near Queenstown in Eastern Cape. His blood had an alcohol content of 1.6 g/100 ml (1.6%). Also in the vehicle were five boys and a woman who were also arrested.
In 2004, an unidentified Taiwanese woman died of alcohol intoxication after immersion for twelve hours in a bathtub filled with 40% ethanol. Her blood alcohol content was 1.35%. It was believed that she had immersed herself as a response to the SARS epidemic.
In Poland, a homeless man was found sleeping half-naked on January 28, 2011, in Cieszyn. His blood had an alcohol level of 1.024%. Despite the temperature of −10 °C and extremely high blood alcohol content, the man survived.
In December 2004, a man was admitted to the hospital in Plovdiv, Bulgaria, after being struck by a car. After detecting a strong alcohol odor, doctors at a hospital conducted a breath test which displayed the man's blood alcohol content at 0.914%. The man was treated for serious injuries sustained in the crash and survived.
In February 2005, French gendarmes from Bourg-en-Bresse, France, conducted a breath test on a man who had lost control of his car. He had an alcohol content of 0.976%. He was not injured in the accident but received a custodial sentence and his driving license was canceled.
In 1982, a 24-year-old woman was admitted to the UCLA emergency room with a serum alcohol concentration of 1.5% (1,510 mg/dL), corresponding to a BAC of 1.33%. She was alert and oriented to person and place. Serum alcohol concentration is not equal to nor calculated in the same way as blood alcohol content.
In 2012, on Oct 26th a man from Olszewo-Borki community, Poland, who died in a car accident, had 2.23%; however, the blood sample was collected from a wound and thus possibly contaminated.
In 2013, on July 26 a 30-year-old man from Alfredówka, Poland, was found by Municipal Police Patrol from Nowa Dęba lying in the ditch along the road in Tarnowska Wola. At the hospital there was recorded that the man had 13.74 permille of alcohol in the blood (1.374%). The man survived.
In 1995, a man from Wrocław caused a car accident near his hometown. He had an alcohol content of 1.48% (14,8 permille) - he was tested five times but all results were the same. He died a few days later of injuries from the accident.
^according to Section 185 of Motor Vehicles Act 1988. On first offence, the punishment is imprisonment of 6 months and/or fine of 2000 Indian Rupees (INR). If the second offence is committed within three years, the punishment is 2 years and/or fine of 3000 Indian Rupees (INR). The clause of 30 mg/dL was added by an amendment in 1994. It came into effect beginning 14 November 1994.
^http://www.npa.go.jp/annai/license_renewal/english.pdf The breath alcohol concentration limit for driving in Japan is 0.15 mg/l, which, assuming a breath alcohol to blood alcohol ratio of 1:2,100, is roughly equivalent to a BAC of 0.0315%. The penalties become even more severe at 0.25 mg/l, which is roughly equivalent to a BAC of 0.0525%.
^Roberts, C.; Robinson, S.P. (2007). "Alcohol concentration and carbonation of drinks: The effect on blood alcohol levels". Journal of Forensic and Legal Medicine14 (7): 398–405. doi:10.1016/j.jflm.2006.12.010. PMID17720590.
^Montgomery, Mark R.; Reasor, Mark J. (1992). "Retrograde extrapolation of blood alcohol data: An applied approach". Journal of Toxicology and Environmental Health36 (4): 281–92. doi:10.1080/15287399209531639. PMID1507264.
^O'Neill, Shane; Tipton, KF; Prichard, JS; Quinlan, A (1984). "Survival After High Blood Alcohol Levels: Association with First-Order Elimination Kinetics". Archives of Internal Medicine144 (3): 641–2. doi:10.1001/archinte.1984.00350150255052. PMID6703836.