BAC Calculator
Estimate your Blood Alcohol Content using the Widmark formula and track calories from drinks
Your Results
Understanding Blood Alcohol Content (BAC)
Blood Alcohol Content, or BAC, is the percentage of alcohol present in your bloodstream. When you consume an alcoholic beverage, alcohol is absorbed through the stomach lining and small intestine into the blood. A BAC of 0.08 percent means that there are 0.08 grams of alcohol per 100 milliliters of blood. This is the legal driving limit in the United States and many other countries. The Widmark formula, developed by Swedish professor Erik Widmark in the 1930s, remains the most widely used method for estimating BAC based on the amount of alcohol consumed, body weight, gender, and time elapsed since drinking.
Several factors influence how quickly your BAC rises and falls. Body weight plays a major role because alcohol distributes through body water, and heavier individuals generally have more water volume to dilute the alcohol. Gender is another significant factor: women typically have a higher proportion of body fat and less body water than men of the same weight, which means alcohol becomes more concentrated in their blood. The Widmark formula accounts for this through gender-specific distribution ratios of 0.73 for men and 0.66 for women.
Your body eliminates alcohol at a relatively constant rate of approximately 0.015 percent BAC per hour, regardless of how much you have consumed. This means that if your BAC is 0.08 percent, it will take roughly five to six hours to return to zero. There is no way to speed up this process - coffee, cold showers, and exercise do not reduce BAC faster. Eating food before or during drinking can slow alcohol absorption and lower peak BAC, but it does not increase the elimination rate. Understanding these facts is critical for making responsible decisions about when it is safe to drive or operate machinery.
Alcohol also carries a significant caloric load that many people overlook. Pure alcohol contains 7 calories per gram, making it nearly as calorie-dense as fat at 9 calories per gram. A standard beer adds roughly 150 calories, a glass of wine around 125 calories, and a shot of spirits about 97 calories before any mixers are added. Mixed cocktails can easily exceed 300 calories each. For anyone managing their weight or following a nutrition plan, tracking alcohol calories alongside food intake is essential. This calculator provides both BAC estimates and calorie totals to give you a complete picture of your alcohol consumption.
How to Use This Calculator
- Select a drink type from the dropdown menu (beer, wine, spirits, or custom) and specify the quantity. Click "Add Drink" to add it to your drink list.
- Continue adding drinks as needed. Each drink appears in the list below and you can remove individual drinks if you make a mistake.
- Enter how many hours have passed since your first drink. This is crucial because your body eliminates alcohol over time.
- Enter your body weight and select the unit (pounds or kilograms). Choose your gender, as this affects the alcohol distribution calculation.
- Click "Calculate BAC" to see your estimated blood alcohol content, time until sober, legal limit comparison, and total calories consumed from your drinks.
Frequently Asked Questions
What is the Widmark formula and how does it work?
The Widmark formula calculates BAC as: (total alcohol in ounces x 5.14) divided by (body weight in pounds x gender constant) minus (0.015 x hours since first drink). The gender constant is 0.73 for males and 0.66 for females, reflecting differences in body water distribution. The 0.015 factor represents the average rate at which the body metabolizes alcohol per hour. This formula was developed by Erik Widmark in the 1930s and remains the standard estimation method used by forensic toxicologists.
What counts as one standard drink?
In the United States, one standard drink contains approximately 0.6 fluid ounces (14 grams) of pure alcohol. This is equivalent to 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. Many popular drinks contain more than one standard drink: a 16-ounce craft IPA at 7% ABV is nearly two standard drinks, and a large glass of wine poured at home is often 7-8 ounces rather than the standard 5.
How accurate is this BAC calculator?
The Widmark formula provides a reasonable estimate, but actual BAC can vary significantly due to factors not captured by the formula. These include your metabolic rate, whether you ate food before or during drinking, your body fat percentage, medications you may be taking, liver health, and individual genetic differences in alcohol-processing enzymes. This calculator should never be used to determine whether it is safe to drive. When in doubt, always use a designated driver, rideshare service, or wait until you are certain the alcohol has been fully metabolized.
How long does it take for alcohol to leave your system?
Your body eliminates alcohol at an average rate of 0.015% BAC per hour. At this rate, it takes approximately one hour to eliminate one standard drink for most people. However, if your BAC reaches 0.08%, it will take roughly 5.3 hours to return to zero. At 0.15%, it would take about 10 hours. These are averages - some people metabolize alcohol slightly faster or slower. No method, including coffee, exercise, or cold water, can speed up alcohol metabolism. Only time allows your body to process and eliminate alcohol.
Why does gender affect BAC?
Gender affects BAC primarily because of differences in body composition. On average, women have a higher percentage of body fat and lower percentage of body water than men of the same weight. Since alcohol distributes through body water but not fat tissue, the same amount of alcohol results in a higher concentration in women. Additionally, women tend to produce less of the stomach enzyme alcohol dehydrogenase, which begins breaking down alcohol before it enters the bloodstream. These biological differences mean women typically reach higher BAC levels than men after consuming the same amount of alcohol relative to body weight.
How many calories are in alcoholic drinks?
Alcohol itself contains 7 calories per gram. A standard 12-ounce beer contains approximately 150 calories, though light beers may have 100 calories and craft beers can exceed 250. A 5-ounce glass of wine averages 125 calories. A 1.5-ounce shot of spirits contains about 97 calories on its own, but mixed drinks add significantly more from sugary mixers, juices, and syrups - a margarita can contain 300 or more calories. For weight management, tracking these liquid calories is just as important as monitoring food intake.
Is it safe to drive if my BAC is below 0.08%?
Not necessarily. While 0.08% is the per se legal limit for adults in most US states, impairment begins well below this threshold. Research shows that reaction time, coordination, and judgment can be measurably affected at BAC levels as low as 0.02%. Many countries set their legal limits much lower - Sweden and Poland use 0.02%, and much of Europe uses 0.05%. For commercial drivers in the US, the limit is 0.04%. For drivers under 21, most states enforce zero tolerance (0.00-0.02%). The safest choice is always not to drive after consuming any amount of alcohol.
