Blood Alcohol Calculator
A blood alcohol calculator estimates your Blood Alcohol Content (BAC) based on your weight, gender, number of drinks, drink type, and time spent drinking. Enter your details in the panel to get an instant BAC estimate using the standard Widmark formula used across the United States.
What Is Blood Alcohol Content (BAC)?
Blood Alcohol Content, or BAC, is the concentration of alcohol in a person's bloodstream expressed as a percentage. A BAC of 0.08% means there are 0.08 grams of alcohol per 100 milliliters of blood. BAC is the standard measure used by law enforcement in the United States and most other countries to determine legal intoxication. It is measured through blood tests, breathalyzers, or urine tests, with breathalyzers being the most common method used during traffic stops.
BAC rises as alcohol is absorbed into the bloodstream through the stomach and small intestine, then falls as the liver metabolizes the alcohol at approximately 0.015% per hour. The rate of absorption and metabolism varies significantly between individuals based on body weight, gender, food consumption, and other factors. If you want to simulate what a breathalyzer device would show, try our online breathalyzer test which presents the same calculation as a virtual breath alcohol reading.
How the BAC Calculator Works
The Widmark Formula Explained
This calculator uses the Widmark formula, the standard method for estimating BAC:
- A — Total pure alcohol consumed in ounces (drinks x 0.6 oz per standard drink)
- W — Body weight in pounds
- r — Gender constant: 0.73 for males, 0.66 for females
- H — Hours elapsed since the first drink
- 5.14 — Conversion factor (alcohol density and volume adjustment)
- 0.015 — Average hourly BAC elimination rate
Understanding the Fields
Each field in the calculator directly affects the Widmark formula result. Heavier individuals have a larger volume of distribution for alcohol, which lowers BAC. Males typically have more body water than females of the same weight, which is why the gender constant differs. The number and type of drinks determines the total pure alcohol consumed, and hours elapsed accounts for the liver's ongoing metabolism.
BAC Levels and Their Effects
| BAC Level | Effects |
|---|---|
| 0.02% | Mild relaxation, slight mood elevation, minor visual impairment |
| 0.05% | Lowered inhibitions, impaired judgment, reduced coordination, difficulty steering |
| 0.08% | Legal intoxication limit in all US states. Significant impairment of muscle coordination, judgment, and reaction time |
| 0.10% | Slurred speech, poor coordination, significantly slowed thinking |
| 0.15% | Major loss of balance, vomiting, severely impaired control |
| 0.20%+ | Disorientation, loss of consciousness risk, alcohol poisoning danger, potential death |
Legal BAC Limits in the United States
Standard 0.08% Limit
Every state in the United States enforces a legal BAC limit of 0.08% for drivers aged 21 and over. At or above this threshold, a driver is considered legally impaired and can be charged with a DUI (Driving Under the Influence) or DWI (Driving While Intoxicated). Some states have lower administrative limits of 0.05% that can result in license suspension even without a criminal charge. The National Highway Traffic Safety Administration reports that drunk driving causes over 10,000 deaths each year in the United States.
Zero Tolerance for Under 21
All 50 states have zero tolerance laws for drivers under 21. The legal BAC limit for underage drivers is 0.00% to 0.02% depending on the state. Any detectable alcohol in an underage driver's system can result in license suspension, fines, and criminal charges. These laws exist because the combination of inexperienced driving and any level of alcohol impairment significantly increases crash risk.
Commercial Driver Limits
Commercial drivers operating vehicles such as trucks, buses, and taxis are held to a stricter limit of 0.04% BAC. This lower threshold reflects the greater responsibility commercial drivers have for public safety and the longer stopping distances required for heavy vehicles. Commercial drivers found over 0.04% face immediate disqualification from operating commercial vehicles in addition to standard DUI penalties.
How Different Drinks Affect Your BAC
Beer vs Wine vs Spirits
Despite common belief, beer, wine, and spirits raise BAC at the same rate when consumed in standard serving sizes, because one standard drink of each contains approximately the same amount of pure alcohol: 0.6 fluid ounces. A 12-ounce beer at 5% ABV, a 5-ounce glass of wine at 12% ABV, and a 1.5-ounce shot of 80-proof spirits each deliver 0.6 ounces of pure ethanol. The difference lies in how quickly these drinks are typically consumed and how their alcohol is absorbed.
Carbonated alcoholic drinks and shots of spirits tend to be absorbed faster than regular beer or wine because carbonation speeds gastric emptying. This can cause a faster initial spike in BAC compared to the same amount of alcohol consumed in a non-carbonated form. According to CDC guidelines on alcohol consumption, there is no safe level of alcohol consumption for driving.
What Counts as One Standard Drink
In the United States, one standard drink contains 14 grams (0.6 fluid ounces) of pure alcohol. This equals: one 12-ounce regular beer (5% ABV), one 5-ounce glass of wine (12% ABV), one 1.5-ounce shot of distilled spirits (40% ABV), or one 8-ounce malt liquor (7% ABV). Many craft beers, large wine pours, and mixed cocktails contain significantly more than one standard drink, which makes it easy to underestimate actual alcohol consumption.
Factors That Affect BAC
The Widmark formula provides an estimate, but actual BAC can vary from the calculated result due to several individual factors:
- Body weight and composition — More body mass means a larger distribution volume for alcohol, lowering BAC. Higher body fat percentage slightly increases BAC since fat tissue contains less water than muscle.
- Gender — Women generally have less body water and lower levels of alcohol dehydrogenase (the enzyme that metabolizes alcohol in the stomach), resulting in higher BAC from the same amount of alcohol.
- Food intake — Eating before or during drinking slows alcohol absorption significantly. A full meal can reduce peak BAC by 30–50% compared to drinking on an empty stomach.
- Metabolism rate — Most people metabolize alcohol at 0.015% BAC per hour, but this can range from 0.01% to 0.03% depending on genetics, liver health, and regular alcohol use.
- Medications — Many prescription and over-the-counter medications interact with alcohol, either amplifying its effects or altering metabolism. Always consult a prescriber before combining alcohol and medications.
- Hydration and fatigue — Dehydration and lack of sleep amplify the subjective effects of alcohol even when BAC is the same as on other occasions.
How Long Does Alcohol Stay in Your System?
The liver metabolizes alcohol at a fixed rate of approximately 0.015% BAC per hour, regardless of how much coffee, water, food, or sleep you consume after drinking. Nothing speeds up this process. A person with a BAC of 0.08% needs approximately 5.3 hours for their BAC to return to zero. Someone at 0.15% needs about 10 hours. Alcohol can be detected in breath for up to 24 hours, in urine for 12 to 24 hours (or longer with ethyl glucuronide tests), and in blood for up to 12 hours after the last drink. For a full hour-by-hour BAC timeline, use our alcohol metabolism calculator. The National Institute on Alcohol Abuse provides detailed information on how alcohol affects the body and metabolism.
BAC Calculator Examples
Example 1 - 180 lb Male, 3 Beers, 2 Hours
A 180-pound male drinks 3 standard beers over 2 hours. Total pure alcohol: 3 x 0.6 = 1.8 oz. BAC = (1.8 x 5.14) / (180 x 0.73) - (0.015 x 2) = 9.252 / 131.4 - 0.03 = 0.0704 - 0.03 = 0.040%. This person is below the legal limit but still has measurable alcohol in their system. They should not assume they are safe to drive, as impairment begins at lower BAC levels for some individuals.
Example 2 - 140 lb Female, 2 Glasses Wine, 1 Hour
A 140-pound female drinks 2 glasses of wine (10 oz total, 12% ABV) over 1 hour. Total pure alcohol: 2 x 0.6 = 1.2 oz. BAC = (1.2 x 5.14) / (140 x 0.66) - (0.015 x 1) = 6.168 / 92.4 - 0.015 = 0.0668 - 0.015 = 0.052%. This is below the 0.08% legal limit, but coordination and judgment are likely impaired. This person should not drive. Use our tip calculator to handle the bill and arrange a safe ride home instead.
Frequently Asked Questions
Is 0.08% legally drunk in every US state?
Yes. All 50 US states enforce a 0.08% BAC legal limit for drivers aged 21 and over. However, some states also have administrative penalties that begin at 0.05%, and drivers under 21 face zero tolerance laws of 0.00% to 0.02% depending on the state.
How many drinks does it take to reach 0.08%?
This depends heavily on body weight, gender, and time. A 120-pound woman may reach 0.08% after just 2 standard drinks in an hour. A 200-pound man may need 4 or more drinks in the same timeframe. Use the calculator above for an estimate based on your specific inputs.
Does coffee lower BAC?
No. Coffee, cold showers, food, and exercise do not lower BAC or speed up alcohol metabolism. Only time reduces BAC. The liver metabolizes alcohol at a fixed rate of approximately 0.015% per hour regardless of what you do. Coffee can make you feel more alert, which may create a false sense of sobriety.
How fast does BAC drop over time?
BAC drops at an average rate of 0.015% per hour. A person at 0.10% BAC would need approximately 6.7 hours to reach 0.00%. Individual metabolism varies from about 0.01% to 0.03% per hour, but 0.015% is the standard estimate used in the Widmark formula.
Can BAC be different for two people who drank the same amount?
Yes, significantly. A 120-pound woman and a 200-pound man who each drink 3 beers in 2 hours can have vastly different BAC readings because of differences in body weight, body water percentage, and the gender constant in the Widmark formula. Tolerance, food intake, and genetics also contribute to these differences.