Blood Alcohol Concentration (BAC) is a precise measurement of the amount of alcohol present in a person's bloodstream. It is expressed as a percentage by weight per unit volume. For example, a BAC of 0.08% means there are 0.08 grams of alcohol for every 100 milliliters of blood. It is the primary scientific and legal standard used worldwide to define alcohol impairment for activities like driving.

“Natural blood alcohol level” typically refers to the blood alcohol concentration (BAC) in healthy individuals who have not consumed any alcoholic beverages or foods. This level is generally below 0.01 mg/dL (milligrams per deciliter), equivalent to 0.00001%. This naturally occurring blood alcohol content is extremely low, far below the detection threshold of standard breathalyzers (typically 0.02% BAC), and is considered “zero” in forensic or traffic testing.
The minute trace amounts of endogenous alcohol present in blood are primarily produced by fermentation from gut microbiota, human metabolism, or, in rare cases, abnormal fermentation within the intestines caused by certain diseases, leading to significant accumulation of alcohol within the body.

In the United States, the legal maximum blood alcohol concentration (BAC) for drivers aged 21 and older is 0.08%. However, lower BAC limits apply in certain jurisdictions and for specific groups, such as: 0.05% in Utah, 0.04% for commercial drivers, and 0.01% to 0.02% for drivers under 21. Drivers may still be charged with driving under the influence even if their blood alcohol concentration is below these limits.

If you are a man weighing between 100-240 lbs, drinking one 12-ounce bottle of beer (5% ABV) will raise your blood alcohol concentration (BAC) to 0.019%-0.045%. It takes approximately 1.3-3 hours for your body to fully metabolize the alcohol from one bottle of beer.
If you are a woman weighing 100-240 lbs, drinking one 12-ounce bottle of beer (5% ABV) will raise your blood alcohol concentration to 0.023%-0.056%. It will take 1.6-3.7 hours for your body to fully metabolize the alcohol from one bottle of beer.

Drinking one glass of wine (12% alcohol, 5 oz) is equivalent to drinking one 12-ounce glass of beer with 5% alcohol. Refer to the answer above for details.

Drinking one shot of hard liquor (40% alcohol, 1.5 oz) is equivalent to drinking one 12-ounce beer with 5% alcohol content. Both share the same metabolism time and blood alcohol concentration. You can directly refer to the answer for one beer.

Blood alcohol concentration (BAC) can be determined through breath, blood, urine, and saliva testing. Breathalyzers are the most commonly used method but not the most accurate. The most precise method involves drawing venous blood and analyzing its ethanol content. Other methods such as PEth testing (blood), saliva testing, and hair testing are less frequently used. While still prone to error, a self-testing method available when these instruments or conditions are unavailable is estimating alcohol concentration using a BAC calculator.

1. Breathalyzer (Breath Test): Typically, drivers suspected of drunk driving are asked to exhale into a breathalyzer, which measures alcohol content in exhaled breath. This provides rapid results with relatively high accuracy.
2. Blood Testing: Analyzed using gas chromatography, enzymatic methods, or the dichromate method. It can measure blood alcohol concentration up to 12 hours after drinking.
3. Urine Testing (EtG/EtS): Detects alcohol consumption within the past 12-24 hours. For heavy drinkers, it can detect consumption up to 72 hours prior.
4. Saliva testing: Measures alcohol concentration in saliva, which correlates closely with blood alcohol levels.
5. Phosphatidylethanol (PEth) testing: This method can detect alcohol consumption from several weeks prior.

When we see police conducting DUI checks on TV, they typically use a breathalyzer device that drivers blow into to detect alcohol impairment. This breathalyzer is essentially a compact, handheld Preliminary Alcohol Screening (PAS) device, such as the Alco Sensor IV, which provides a rapid estimate of blood alcohol content. If the reading exceeds the legal limit, the driver is taken to the police station for an official confirmation test using a larger, more precise Evidential Breath Testing (EBT) device, like the Intoxilyzer 8000. This equipment provides printed results that serve as formal evidence in court, meeting stricter legal standards.

1. Gray-cap tubes (preferred): Contain sodium fluoride (preservative) and potassium oxalate (anticoagulant) to prevent blood cell breakdown and alcohol consumption.
2. Red-cap tubes (standard or gel-type): Used for serum separation, typically as an alternative when gray caps are unavailable, but require immediate separation from cells for medical testing.
3. Lavender/Pink Cap Tubes (EDTA): Contain the anticoagulant EDTA and are accepted by certain laboratories, particularly routine chemistry/hematology labs.
4. Green Cap Tubes (Heparin): Used for plasma testing and occasionally for medical alcohol testing (STAT).

The average rate of decrease in blood alcohol concentration (BAC) is 0.015% per hour. The human body's rate of alcohol metabolism is relatively stable and is generally unaffected by other factors such as cold showers, coffee, exercise, or fresh air, which do not accelerate the metabolic process.

The human body typically requires approximately 1.3 to 3.7 hours to metabolize one standard drink (12 ounces of beer, 5 ounces of wine, or 1.5 ounces of spirits). If blood alcohol concentration reaches 0.08% after drinking, it takes over 5 hours to reduce it back to 0.00%.

The blood alcohol concentration (BAC) in a healthy human body is extremely low, almost negligible. However, when you consume alcohol or alcohol-containing foods too quickly—exceeding the liver's ability to metabolize it—the BAC gradually rises. Several factors influence blood alcohol concentration:

1. Rate of consumption: Rapid drinking, gulping, binge drinking, or consuming large quantities of alcoholic foods can overload the liver, leading to rapid alcohol accumulation.
2. Consumption rate: The more alcohol you drink and the faster you consume it, the higher your BAC will be, as the liver can metabolize approximately one alcoholic drink per hour.
3. Empty stomach: Food slows alcohol absorption; on an empty stomach, alcohol enters the bloodstream more rapidly.

Since the liver's rate of alcohol metabolism is relatively stable, it is recommended to slow down alcohol intake by eating before and after drinking. Additionally, alternating alcoholic beverages with water during drinking helps maintain adequate hydration and prevents rapid increases in blood alcohol concentration. Remember to control your drinking pace—avoid drinking too quickly, otherwise BAC will still rise rapidly.

After drinking, your blood alcohol concentration (BAC) begins to impair your judgment when it reaches 0.02%. As you consume more alcohol, this concentration rises. At around 0.05%, more pronounced impairment and reduced inhibitions typically occur. In many countries and regions, 0.08% is the legal threshold for impaired driving (DUI/DWI). Reaching 0.10%–0.12% leads to noticeable lack of coordination, impaired judgment and memory, and difficulty with motor skills.

When your BAC reaches 0.15 to 0.30 g%, your life is at high risk. Potential symptoms include difficulty breathing, inability to walk independently, loss of bladder control, and even unconsciousness.
Some friends who enjoy drinking may also frequently ask, “What blood alcohol level causes death?” or “What blood alcohol level leads to blackout?” A lethal blood alcohol level is a BAC exceeding 0.30 g%, which makes it extremely likely for a person to lose consciousness, fall into a coma, or even die.

When blood alcohol concentration (BAC) reaches 0.30% to 0.40%, the body is highly likely to be in a state of alcohol intoxication. This condition is extremely dangerous, often leading to loss of consciousness and posing a life-threatening risk. When BAC exceeds 0.40%, the mortality rate becomes extremely high.

The highest recorded blood alcohol concentration (BAC) among documented survivors was 1.374% (13.74 g/L). This was a 40-year-old Polish man discovered in July 2013 in a state of alcohol poisoning, unconscious. Fortunately, he ultimately survived.
An even higher record exists: a 28-year-old Polish man discovered with a BAC of 1.480% (14.8 g/L). However, he died from injuries sustained in a car accident, not alcohol poisoning. This further underscores that countless accidents occur annually due to drunk driving. For your safety and the safety of others, never drink and drive. Stay safe.