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Updated on February 2, 2023
6 min read

BAC Definition

BAC (Blood Alcohol Concentration) Definition

Blood alcohol concentration (BAC) measures the alcohol (ethyl alcohol or ethanol) in the bloodstream. Presented as a percentage, BAC reflects how fast the body absorbs, distributes, metabolizes, and excretes alcohol.

A person who consumes more than one alcoholic drink in an hour will have a higher BAC than someone who only consumes one drink per hour. If a person stops consuming alcohol, is unconscious, and still has alcohol in their gastrointestinal tract (GI), their BAC can still increase.

The body will continue to absorb the remaining alcohol in the GI tract. Therefore, the body will continue to release alcohol into the bloodstream and circulate it.

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The Effects of Different Levels of BAC

The effects of alcohol on the body will depend on the blood alcohol level. The liver can only process approximately one standard drink per hour.

In most cases, one standard drink is:

  • 12 ounces (oz.) of 6% ABV beer
  • 5 oz. of wine
  • 1.5 oz. of whiskey

The higher your BAC levels are, the more side effects you will feel from alcohol.

  • BAC 0.0%: You are sober. You don’t have any alcohol in your system.
  • BAC 0.02%: You may start to feel slightly altered. You may feel your mood change or experience a loss of judgment.
  • BAC 0.05%: You may begin to feel uninhibited, less alert, and increased impaired judgment.
  • BAC 0.08%: You may lose muscle coordination, participate in more risky behavior, and even more impaired reasoning and judgment.
  • BAC 0.10%: You may have a slowed reaction time, mumbled or slurred speech, and confused thinking.
  • BAC 0.15%: You may experience a shift in mood, nausea, vomiting, inability to balance, and uncontrollable muscle movement.
  • BAC 0.15% to 0.30%: You may experience vomiting, heightened confusion, and tiredness.
  • BAC 0.30% to 0.40%: You may lose consciousness or have alcohol poisoning, a possibly life-threatening condition.
  • BAC Over 0.40%: This is a potentially deadly BAC. You’re at risk of coma and death from cardiac arrest.

BAC Testing

BAC testing involves using a blood test. People get it for various reasons.

What To Expect During a BAC Test

A healthcare provider will administer the blood test through a vein on the inner part of your arm. They will clean the area and insert the needle into your vein, causing a slight pinching sensation.

The healthcare provider will draw a small amount of blood into a test tube. Once they’ve collected enough blood, they will remove the needle and place gauze or a cotton ball at the insertion spot to stop bleeding. 

Finally, they will place a bandage over the top. The entire procedure usually takes around 5 minutes.

What Situations Require a BAC Test

Someone may get their BAC tested for one of these reasons:

  • To monitor AUD: Treatment centers may have you undergo BAC tests to ensure sobriety.
  • Medical testing: A healthcare provider may use a BAC test if you arrive at the hospital for alcohol poisoning.
  • Work: An employer may ask employees to get a BAC test to ensure they’re not drinking on the job.
  • Legal testing: You may need to get a BAC test if you’re under legal investigation for drunk driving or underage drinking

Understanding BAC Test Results

BAC test results usually come out in percentages, like:

  • 0.04%
  • 0.08%
  • 0.10%

However, they can also register as grams per milliliter (g/mL). This would show up as 0.04 g/100 mL. Sometimes, test results come back positive or negative.

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5 Factors That Affect Blood Alcohol Content

BAC relates to the body’s ability to absorb and break down alcohol. It is essential to consider factors that may influence absorption and metabolism.

1. Amount of Alcohol (Number of Standard Drinks) 

The amount of alcohol in a person’s blood will contribute to their BAC. The liver can metabolize one standard drink (14 grams of pure alcohol) in an hour.

If a person consumes more than one alcoholic beverage in that time frame, BAC will increase. This is especially true for those who partake in binge or heavy drinking.

  • Binge drinking: Men consume five or more drinks within 2 hours, while women consume four or more drinks.
  • Heavy drinking: Men consume four or more drinks on any given day, while women consume three or more drinks.

In both scenarios, a large amount of alcohol in the body overwhelms metabolic processes and results in elevated BACs in little time.

2. Gender

Women face more difficulty in metabolizing alcohol than men. As a result, women will have higher BACs faster than men. 

This occurs as a result of the following:

  • Body composition: Women have a higher percentage of body fat and a lower percentage of water than men. Alcohol does not dissolve in fat, so there becomes a build-up of alcohol in the bloodstream.
  • Stomach ADH (alcohol dehydrogenase): ADH  is an alcoholic-metabolizing enzyme that is not prevalent in a woman's stomach. Consequently, women do not metabolize as much alcohol before it enters the bloodstream.
  • Liver ADH: ADH in a woman’s liver does not perform as efficiently in breaking down alcohol as in a man’s liver, which contributes to a rise in BAC.
  • Hormones: Hormones can affect a person’s ability to metabolize alcohol. When a woman has her period, she may have a higher BAC due to hormone fluctuations.

3. Body Weight

Weight can determine how alcohol diffuses in the body. For example, a person who weighs 130 pounds can consume two beers and have a lower BAC than someone who drinks the same amount of beverages but weighs less.

Similarly, a person with more muscle mass will be able to absorb and metabolize alcohol better than someone with a higher body fat percentage. Again, alcohol does not dissolve in fat.

4. Body Size

Body size can also determine how quickly alcohol is absorbed and metabolized. Those with a more petite body frame have higher BACs than people with larger bodies, even when alcohol consumption is the same. 

5. Stomach Contents

Drinking on an empty stomach can contribute to a higher BAC. Eating before drinking, especially food high in protein, is recommended to slow the absorption of alcohol.

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Legal BAC Levels While Driving

In 49 US states, driving with a BAC of 0.08% or higher is illegal. The risk of alcohol-related car crashes exponentially grows when BAC is 0.08% or higher. 

In Utah, since 2019, the maximum legal BAC is 0.05%. A person with a BAC of 0.05% can begin having trouble steering the wheel or responding to emergencies. 

When someone has a BAC of 0.08%, different effects of alcohol may occur. These include:

  • Poor muscle coordination, such as balance, speech, or reaction team
  • Impaired judgment, self-control, and reasoning
  • Short-term memory loss
  • Difficulty in detecting danger

These effects translate into speed control issues and limited information-processing capabilities like signal detection. Additionally, it is illegal for those under 21 to be driving with a BAC of at least 0.01%

It is important to remember that even if someone doesn't exceed the legal alcohol limit, there is still a risk of alcohol-related traffic accidents. In 2020, there were 2,041 people killed in alcohol-related crashes where a driver had a BAC of 0.01 to 0.07 g/dL.8

Risks of Driving Under The Influence (DUI)

When people decide to drive under the influence, they run the risk of suffering undesirable, possibly life-threatening events. These events include:

  • Alcohol-related traffic accidents
  • Unintentional physical or emotional harm to others
  • Manslaughter 
  • Jail 
  • Hefty fines 
  • Suspended or revoked driver’s license
  • A sudden spike in car insurance fees

Planning before drinking is essential to avoid the adverse circumstances above. If you believe that you will consume alcohol, avoid driving a vehicle.If you believe you suffer from alcohol dependence or abuse, it is crucial to seek professional medical help. Healthcare specialists can help guide you through withdrawal, minimize your risk of overdose, and set you on your path to recovery.

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Updated on February 2, 2023
7 sources cited
Updated on February 2, 2023
All Alcoholrehabhelp content is medically reviewed or fact checked to ensure as much factual accuracy as possible.

We have strict sourcing guidelines and only link to reputable media sites, academic research institutions and, whenever possible, medically peer reviewed studies.
  1. Alcohol // Rev. James E. McDonald, C.S.C., Center for Student Well-Being // University of Notre Dame.” Rev. James E. McDonald, C.S.C., Center for Student Well-Being, 2020.
  2. Drunk Driving.” NHTSA, 2020.
  3. Impaired Driving: Get the Facts.” Centers for Disease Control and Prevention, 2019.
  4. Module 1: Gender Matters.” The Alcohol Pharmacology Education Partnership, Duke University.
  5. Olson et al. “Relationship Between Blood Alcohol Concentration and Observable Symptoms of Intoxication in Patients Presenting to an Emergency Department.” OUP Academic, Oxford University Press, 2013.
  6. Understanding the Dangers of Alcohol Overdose.” National Institute on Alcohol Abuse and Alcoholism, U.S. Department of Health and Human Services, 2020.
  7. Zakhari, S. "Overview: How Is Alcohol Metabolized by the Body?" National Institute on Alcohol Abuse and Alcoholism, 2006.

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