Last updated: March 2026
What is Blood Alcohol Content (BAC)?
Blood Alcohol Content (BAC) is the percentage of alcohol in your bloodstream by weight. A BAC of 0.08% means there are 0.08 grams of alcohol per 100 milliliters of blood. It's the standard legal measurement used worldwide to determine intoxication levels and driving impairment.
BAC rises as you consume alcohol and falls as your body metabolizes it. The rate of rise depends on how quickly you drink, your body weight, gender, and whether you've eaten. The rate of decline is remarkably consistent: approximately 0.015% per hour, regardless of body size. This is because alcohol metabolism is primarily limited by liver enzyme activity, which doesn't scale with body weight.
In the United States, the legal BAC limit for driving is 0.08% in all 50 states. However, impairment begins well below this threshold. At 0.02%, you may experience altered mood and slight loss of judgment. By 0.05%, coordination and the ability to track moving objects are measurably impaired. The legal limit is not a safe limit — it's a criminal threshold.
How BAC is Calculated
This calculator uses the Widmark formula, developed by Swedish physician Erik Widmark in the 1930s. The formula estimates BAC based on the amount of alcohol consumed, body weight, a gender-specific distribution factor, and time elapsed.
The calculation converts each drink into grams of pure alcohol (volume × ABV × density), divides by body weight in grams multiplied by the Widmark factor (0.68 for males, 0.55 for females), then subtracts 0.015% for each hour since drinking began. The Widmark factor represents the proportion of body mass in which alcohol distributes — essentially the water content of the body.
According to NHTSA data, 37 people die every day in drunk-driving crashes in the United States — one person every 39 minutes. In 2022, 13,524 people were killed in alcohol-impaired driving crashes, accounting for 32% of all traffic-related deaths.
BAC Legal Limits by Country
Legal BAC limits vary significantly worldwide. The United States, Canada, and the UK (except Scotland) set their limit at 0.08%. Most of Europe, including France, Germany, and Spain, use 0.05%. Sweden, Norway, and Poland enforce 0.02%, while countries like Hungary, Czech Republic, and Romania maintain a strict 0.00% policy for all drivers.
Australia and most of South America use 0.05%. Japan and China both enforce 0.03%. Many countries have even stricter limits for new drivers, commercial drivers, or drivers under a certain age. The global trend is toward lower limits, as research consistently shows impairment begins well below 0.08%.
Factors That Affect BAC
While this calculator accounts for weight, gender, drinks, and time, many other factors influence your actual BAC. Food in your stomach slows alcohol absorption significantly — drinking on an empty stomach can produce a peak BAC up to 20% higher than drinking after a meal.
Medications can interact with alcohol and alter its effects. Antihistamines, antidepressants, pain medications, and many other drugs amplify alcohol's impact. Body composition matters too: muscle tissue contains more water than fat, so two people of the same weight but different body fat percentages will have different BACs from the same drinks.
Fatigue, stress, hydration level, carbonation in drinks (which speeds absorption), and even altitude can all affect how alcohol impacts you. These are just some of the reasons why no calculator can tell you whether you are safe to drive. The only reliable way to know your exact BAC is with a calibrated breathalyzer or blood test.
Health & Legal Disclaimer: This BAC calculator is for educational and informational purposes only. It provides estimates based on average metabolic rates and cannot account for individual variation. Never use this tool to determine whether you are safe to drive or operate machinery. Alcohol affects everyone differently. When in doubt, do not drive. If you or someone you know needs help with alcohol use, contact SAMHSA's National Helpline at 1-800-662-4357.
Frequently Asked Questions
How accurate is a BAC calculator?
BAC calculators provide rough estimates based on the Widmark formula, which uses average metabolism rates. Actual BAC can vary by 20-30% depending on food intake, medications, liver health, hydration, body composition, and individual metabolism. Never use a calculator to decide if you're safe to drive.
What is the legal BAC limit for driving?
In all 50 US states, the legal limit is 0.08% for drivers 21 and older. For commercial drivers, it's 0.04%. For drivers under 21, most states have zero-tolerance laws (0.00-0.02%). Many countries have lower limits — in Europe, 0.05% is common, and some countries enforce 0.02% or 0.00%.
How long does it take for BAC to reach 0.00%?
The body metabolizes alcohol at approximately 0.015% BAC per hour, regardless of body size. This means a BAC of 0.08% takes roughly 5.3 hours to return to zero. Coffee, cold showers, and exercise do NOT speed up alcohol metabolism — only time works.
What is a 'standard drink'?
A US standard drink contains about 0.6 fluid ounces (14 grams) of pure alcohol. This equals roughly 12oz of regular beer (5% ABV), 5oz of wine (12% ABV), or 1.5oz of distilled spirits (40% ABV). Many cocktails and craft beers contain more alcohol than one standard drink.
Why does gender affect BAC?
Biological sex affects BAC because of differences in body composition and the enzyme alcohol dehydrogenase. Women typically have a higher body fat percentage and lower water content, meaning alcohol is distributed in less body water, resulting in higher BAC from the same amount of alcohol. The Widmark factor accounts for this: 0.68 for males, 0.55 for females.
Does eating food lower your BAC?
Eating before or while drinking slows alcohol absorption, which can result in a lower peak BAC. However, food does not eliminate alcohol — it only delays absorption. A full stomach can reduce peak BAC by up to 20%, but the total alcohol consumed will still be metabolized over time.