How to use the BAC calculator
Start by entering your body weight in pounds and selecting your biological gender. These two inputs determine how alcohol distributes through your body, since the Widmark formula uses body water ratio as a key variable. Males typically have a higher body water percentage (about 73%) compared to females (about 66%), which means the same amount of alcohol will produce a higher BAC reading in someone with less body water.
Next, add the drinks you've consumed. Select from common presets like beer, wine, or a shot of spirits, or choose "Custom" to specify your own ABV and serving size. You can add multiple drink entries to model a realistic drinking session—for example, two beers and one glass of wine. Adjust the quantity, ABV percentage, and ounce size for each entry to match what you actually drank.
Finally, set the number of hours since you started drinking. The calculator subtracts 0.015% BAC per hour to account for your body's alcohol metabolism. This is the average elimination rate used in forensic toxicology. The result is an estimated BAC along with an impairment level, time-to-sober estimate, and legal limit reference. Remember: this is an educational estimate, not a legal or medical measurement.
Understanding the Widmark formula
The Widmark formula is the most widely used method for estimating BAC. It was developed by Swedish researcher Erik Widmark in the 1930s and remains the foundation of forensic BAC estimation. The formula calculates BAC as the total grams of alcohol consumed divided by body weight in grams multiplied by a gender-specific body water constant, then subtracts the metabolic elimination rate multiplied by hours elapsed.
The body water constant (r) is typically 0.73 for males and 0.66 for females, reflecting average body composition differences. The metabolic elimination rate of 0.015% per hour is a population average—individual rates can range from 0.010% to 0.025% depending on liver enzyme activity, genetic factors, and drinking history.
One standard drink in the United States contains approximately 14 grams of pure alcohol. That's the amount in 12 ounces of regular beer at 5% ABV, 5 ounces of wine at 12% ABV, or 1.5 ounces of distilled spirits at 40% ABV (80 proof). Many craft beers, cocktails, and poured drinks exceed these standard sizes, which is why this calculator lets you customize each entry.
Factors that affect real BAC
While the Widmark formula provides a useful estimate, actual BAC is influenced by many factors this calculator cannot account for. Food intake slows alcohol absorption significantly—drinking on a full stomach can reduce peak BAC by 20–40% compared to drinking on an empty stomach. The type of food matters too: high-protein and high-fat meals slow gastric emptying more effectively.
Medications can interact with alcohol metabolism. Common drugs like aspirin, acetaminophen, and antihistamines can alter how quickly your body processes alcohol. Chronic heavy drinkers often develop increased metabolic tolerance, meaning their liver enzymes process alcohol faster, but this doesn't reduce impairment in a linear way. Genetic variations in alcohol dehydrogenase enzymes create substantial differences between individuals and populations.
Hydration level, sleep quality, and overall health also affect how you experience a given BAC level. Two people with identical BAC readings can show very different levels of impairment. This is why BAC estimates should never be used to determine whether someone is safe to drive. The only safe amount of alcohol before driving is zero.
Frequently Asked Questions
What is BAC?
Blood Alcohol Content (BAC) measures the percentage of alcohol in your bloodstream. A BAC of 0.08% is the legal limit for driving in most US states. BAC depends on weight, gender, number of drinks, alcohol content, and elapsed time since drinking.
How accurate is a BAC calculator?
Online BAC calculators provide rough estimates using the Widmark formula. Actual BAC can vary based on metabolism, food intake, medications, hydration, liver function, and individual physiology. For legal or safety decisions, use a certified breathalyzer.
How long does it take to sober up?
The body metabolizes alcohol at roughly 0.015% BAC per hour. A BAC of 0.08% takes about 5.3 hours to reach zero. Nothing speeds up metabolism—not coffee, cold showers, or food. Only time works.
Why does gender affect BAC?
Biological males and females have different average body water ratios. Males average about 73% body water while females average about 66%. Since alcohol distributes through body water, the same amount of alcohol produces a higher BAC in someone with less body water.
What does 'one standard drink' mean?
In the US, one standard drink contains about 14 grams of pure alcohol. That's roughly 12 oz of beer at 5% ABV, 5 oz of wine at 12% ABV, or 1.5 oz of spirits at 40% ABV. Many cocktails and craft beers contain more than one standard drink.
Is it safe to drive at any BAC level?
Impairment begins below the legal limit. Even a BAC of 0.02% can reduce visual function and multitasking ability. The safest choice is not to drive after consuming any alcohol. Use a designated driver or rideshare service.
Disclaimer and methodology
This tool runs entirely in your browser. It uses the Widmark formula with standard body water ratios and a 0.015% per hour elimination rate. Results are educational estimates only—not medical advice, legal evidence, or a substitute for a certified breathalyzer. Never use this calculator to decide whether you are safe to drive. If you have consumed any alcohol, arrange a safe ride home.