Last updated March 2026
BAC Calculator
Estimate your blood alcohol concentration (BAC) based on drinks consumed, body weight, gender, and time elapsed.
What Is BAC?
Blood Alcohol Concentration (BAC) is the percentage of alcohol present in your bloodstream. A BAC of 0.08% means that there are 0.08 grams of alcohol per 100 milliliters of blood. BAC is the standard measurement used by law enforcement, medical professionals, and researchers to quantify alcohol intoxication.
When you consume an alcoholic beverage, the alcohol is absorbed through the stomach lining and small intestine into the bloodstream. From there, it circulates throughout the body, affecting the central nervous system. BAC rises as you drink and falls as your liver metabolizes the alcohol. Understanding your BAC helps you make informed decisions about driving, operating machinery, and general safety.
BAC is influenced by many factors beyond just the number of drinks you consume. Body weight, biological sex, the rate of drinking, whether you have eaten, medications, and individual metabolism all play significant roles. This calculator uses the Widmark formula, the most widely accepted scientific method for estimating BAC, to give you an approximation based on the most impactful variables.
How BAC Is Calculated
BAC estimation relies on the relationship between the amount of alcohol consumed, your body composition, and the time your body has had to metabolize the alcohol. The core calculation accounts for alcohol absorption and elimination:
- Alcohol consumed: Each standard drink contains roughly 14 grams of pure ethanol. The total grams of alcohol are calculated from the number and type of drinks.
- Body water distribution: Alcohol distributes through body water. Since body water percentage differs between males and females, a gender-specific distribution ratio is used.
- Time-based elimination: The liver metabolizes alcohol at a near-constant rate of approximately 0.015 BAC per hour. This amount is subtracted from the calculated peak BAC.
The result is an estimate of the alcohol remaining in your bloodstream at the time specified. Keep in mind that this is a mathematical model — real-world BAC can vary based on genetics, liver health, hydration, food intake, and more.
The Widmark Formula
Erik Widmark, a Swedish physician, developed the foundational formula for estimating BAC in the 1930s. The Widmark formula remains the most commonly cited BAC estimation method in forensic science and toxicology. The formula used in this calculator is:
BAC = (Alcohol in grams / (Body weight in grams × r)) − (0.015 × hours) In this formula, r is the Widmark distribution ratio, which accounts for the proportion of body weight in which alcohol distributes. The values are:
- r = 0.68 for males (higher water content relative to body weight)
- r = 0.55 for females (lower water content, higher proportion of body fat)
The constant 0.015 represents the average rate at which the liver eliminates alcohol from the bloodstream per hour. For one standard drink (14 grams of alcohol), this means it takes roughly one hour for your body to process the alcohol. The formula subtracts this elimination rate multiplied by the number of hours since you began drinking.
For example, a 160-pound male who has consumed 3 standard drinks over 1 hour would have an estimated BAC of approximately: (3 × 14) / (72,575 × 0.68) − (0.015 × 1) = 0.0685 or about 0.069%.
Factors That Affect BAC
While the Widmark formula provides a useful estimate, many factors can cause your actual BAC to differ from the calculated value:
- Body weight and composition: Heavier individuals generally have a lower BAC after the same number of drinks. People with more muscle and less fat tend to have lower BAC because muscle tissue contains more water, which dilutes the alcohol.
- Biological sex: Women typically reach higher BAC levels than men of the same weight after consuming the same amount of alcohol. This is due to differences in body water content, body fat percentage, and the enzyme alcohol dehydrogenase.
- Food intake: Drinking on an empty stomach causes faster alcohol absorption, leading to higher peak BAC. Food in the stomach slows absorption and can reduce peak BAC by up to 20%.
- Rate of consumption: Drinking rapidly produces a higher peak BAC than sipping the same amount over several hours, because the liver can only process about one standard drink per hour.
- Medications: Many medications interact with alcohol and can intensify its effects or slow its metabolism, including antihistamines, painkillers, antidepressants, and antibiotics.
- Tolerance: Regular drinkers may develop functional tolerance, meaning they appear less impaired at a given BAC. However, their BAC is still the same, and their driving and cognitive abilities are still degraded.
- Age: Older adults tend to reach higher BAC levels because of reduced body water content and slower metabolism.
- Genetics: Variations in the genes coding for alcohol dehydrogenase and aldehyde dehydrogenase enzymes affect how quickly individuals metabolize alcohol.
BAC Levels and Their Effects
The following table describes the typical effects of alcohol at various BAC levels. Individual responses vary, but these ranges are based on well-established clinical research:
| BAC Range | Level | Typical Effects |
|---|---|---|
| 0.00 – 0.02% | Sober | Little to no noticeable effects. Normal behavior and coordination. |
| 0.02 – 0.04% | Mildly Relaxed | Slight euphoria, mild relaxation. Subtle impairment of judgment. |
| 0.04 – 0.08% | Buzzed / Impaired | Lowered inhibitions, impaired coordination, reduced reaction time. Feeling of warmth and sociability. |
| 0.08 – 0.15% | Legally Impaired | Significant impairment of motor control and judgment. Slurred speech, poor balance. Illegal to drive in all U.S. states. |
| 0.15 – 0.30% | Severely Impaired | Major loss of balance and coordination. Nausea, vomiting, blurred vision. High risk of blackout. |
| 0.30%+ | Dangerous / Life-Threatening | Loss of consciousness, risk of alcohol poisoning, respiratory depression. Medical emergency likely. |
Legal BAC Limits by Country
Most countries enforce a maximum legal BAC for operating a motor vehicle. Exceeding the limit results in criminal charges, license suspension, fines, and potentially jail time. Here are the limits in several major countries:
- United States: 0.08% in all 50 states (0.04% for commercial drivers, 0.00-0.02% for under-21 drivers)
- Canada: 0.08% federal limit; many provinces enforce penalties starting at 0.05%
- United Kingdom: 0.08% in England and Wales; 0.05% in Scotland
- Australia: 0.05% for full license holders; 0.00% for learner and provisional drivers
- Germany: 0.05% general limit; 0.00% for new drivers (first 2 years)
- Japan: 0.03% — one of the strictest limits among major countries
- Sweden, Norway, Poland: 0.02% — effectively a zero-tolerance approach
- Brazil, Czech Republic, Hungary: 0.00% — absolute zero tolerance
Even if your estimated BAC is below the legal limit, your driving ability may still be impaired. Research consistently shows that reaction time, peripheral vision, and decision-making are affected at BAC levels well below 0.08%.
How Your Body Processes Alcohol
When you consume alcohol, it travels to your stomach and small intestine where it is absorbed into the bloodstream. About 20% of alcohol is absorbed through the stomach lining, and the remaining 80% through the small intestine. Once in the blood, alcohol is distributed throughout the body, with higher concentrations in organs with rich blood supply like the brain and liver.
The liver is responsible for metabolizing approximately 90-95% of the alcohol you consume. The primary enzyme involved is alcohol dehydrogenase (ADH), which converts ethanol to acetaldehyde — a toxic compound. Acetaldehyde is then further broken down by aldehyde dehydrogenase (ALDH) into acetate, which is eventually converted to carbon dioxide and water.
The remaining 5-10% of alcohol is eliminated unchanged through breath, urine, and sweat. This is why breathalyzers can measure BAC — the alcohol in your bloodstream is released into the air in your lungs in a predictable ratio.
The liver processes alcohol at a fairly constant rate regardless of how much you have consumed. For most people, this rate is approximately 0.015 BAC per hour, which translates to roughly one standard drink per hour. Drinking faster than your liver can metabolize alcohol causes BAC to rise. No amount of coffee, cold showers, or exercise can speed up this process.
Standard Drink Sizes
Understanding what constitutes a "standard drink" is essential for accurate BAC estimation. In the United States, one standard drink contains approximately 14 grams (0.6 ounces) of pure ethanol. The following are equivalent to one standard drink:
- Beer: 12 ounces of regular beer at 5% ABV. Craft beers often range from 6-12% ABV, meaning a single pint could equal 1.5 to 2.5 standard drinks.
- Wine: 5 ounces of wine at 12% ABV. A typical restaurant pour may be 6 ounces, and many wines range from 13-15% ABV.
- Spirits: 1.5 ounces of distilled spirits (vodka, whiskey, rum, gin, tequila) at 40% ABV (80 proof). Mixed drinks often contain more than 1.5 ounces of liquor.
- Malt liquor: 8-9 ounces at 7% ABV. A typical 40-ounce bottle of malt liquor contains about 4.5 standard drinks.
One of the most common mistakes in estimating BAC is underestimating the number of standard drinks consumed. A large cocktail at a bar may contain 2-3 standard drinks worth of alcohol. A 16-ounce craft IPA at 8% ABV equals about 2.1 standard drinks. Always check the ABV and serving size to make an accurate count.
Safety Considerations
This BAC calculator is designed as an educational tool to help you understand the relationship between alcohol consumption and blood alcohol concentration. It should never be used as the sole basis for deciding whether it is safe to drive or operate machinery. Important safety points to remember:
- Estimates are not exact: Your actual BAC can be higher or lower than the calculated value depending on many individual factors.
- Impairment begins before the legal limit: Coordination, judgment, and reaction time are affected at BAC levels well below 0.08%.
- Plan ahead: Designate a sober driver, use a ride-share service, or take public transportation if you plan to drink.
- Alcohol poisoning is a medical emergency: If someone is unconscious, vomiting while passed out, has slow or irregular breathing, or has a BAC above 0.30%, call emergency services (911) immediately.
- Wait it out: Only time reduces BAC. There are no shortcuts — coffee, food, and water will not lower your BAC faster.
- Know your limits: Everyone metabolizes alcohol differently. What feels manageable for one person may be dangerous for another.
If you or someone you know is struggling with alcohol consumption, help is available. Contact the SAMHSA National Helpline at 1-800-662-4357 for free, confidential treatment referrals.
Frequently Asked Questions
How long does it take for BAC to reach 0.00?
Your body eliminates alcohol at roughly 0.015 BAC per hour. To estimate how long until your BAC reaches zero, divide your current BAC by 0.015. For example, a BAC of 0.08 would take about 5 hours and 20 minutes. A BAC of 0.15 would take about 10 hours. These are averages — individual metabolism varies.
What is a standard drink?
In the United States, a standard drink contains about 14 grams of pure alcohol. This is equivalent to 12 ounces of beer (5% ABV), 5 ounces of wine (12% ABV), or 1.5 ounces of spirits (40% ABV). Many drinks served at bars and restaurants exceed these sizes, so it is common to consume more standard drinks than you realize.
Is a BAC of 0.05 safe to drive?
No amount of alcohol is truly safe for driving. At 0.05% BAC, studies show measurable impairment in steering, tracking moving objects, and responding to emergencies. While 0.08% is the legal limit in most U.S. states, many countries enforce a 0.05% or lower limit. The only safe BAC for driving is 0.00%.
Related Calculators
- Calorie Calculator — Calculate your daily calorie needs.
- BMI Calculator — Check your Body Mass Index.
- Water Intake Calculator — Find your daily hydration target.