BAC Calculator
Estimate your blood alcohol content (BAC) based on drinks consumed, body weight, gender, and time elapsed.
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What Is a BAC Calculator?
IMPORTANT DISCLAIMER: This calculator provides estimates only and should never be used to determine whether it is safe to drive, operate machinery, or make safety-critical decisions. Blood alcohol content varies significantly between individuals based on genetics, food intake, medications, liver function, hydration, and many other factors that no calculator can account for. The only reliable way to determine your BAC is with a calibrated breathalyser or blood test. When in doubt, do not drive. Use a designated driver, taxi, or rideshare service.
Blood Alcohol Content (BAC) is a measurement of the amount of alcohol present in your bloodstream, expressed as a percentage by weight. A BAC of 0.08% means there are 0.08 grams of alcohol per 100 millilitres of blood. Most countries set legal driving limits between 0.02% and 0.08% BAC, though impairment begins well before the legal limit. Even at 0.02% BAC, studies show measurable decline in divided attention and visual function.
This calculator uses the Widmark formula, developed by Swedish physician Erik Widmark in the 1930s and still widely used in forensic toxicology. It estimates BAC based on the amount of alcohol consumed, your body weight, a gender-specific distribution ratio (men have more body water, which dilutes alcohol more effectively), and the time elapsed since drinking. The body metabolises alcohol at an approximately constant rate of 0.015% BAC per hour, regardless of how much you have consumed.
How Do You Use This BAC Calculator?
Enter the number and type of drinks consumed, your body weight, your gender, and the time elapsed since your first drink to estimate your current blood alcohol content.
- Enter the number of standard drinks consumed (one standard drink = 14 g of pure alcohol in the US, 10 g in many other countries).
- Select the type of drinks or enter the alcohol content and volume manually.
- Enter your body weight in kilograms or pounds.
- Select your gender (biological sex affects alcohol distribution in the body).
- Enter the number of hours since your first drink.
- Review your estimated BAC and the time until it returns to zero — remembering this is an estimate only.
How Does the BAC Calculator Formula Work?
The formula used: BAC = (Alcohol consumed in grams / (Body weight in grams * r)) * 100 - (0.015 * hours since first drink), where r = 0.68 (men) or 0.55 (women)
The Widmark formula estimates BAC based on alcohol consumed, body weight, a gender-specific body water constant, and metabolic elimination over time.
BAC (%) = (Alcohol in grams / (Body weight in grams * r)) * 100 - (Elimination rate * Hours)
Where r = 0.68 for men and r = 0.55 for women (Widmark factors reflecting the proportion of body weight that is water), and the average elimination rate is 0.015% per hour. One US standard drink contains 14 grams of pure alcohol (equivalent to 355 ml of 5% beer, 150 ml of 12% wine, or 44 ml of 40% spirits). Many other countries define a standard drink as 10 grams of alcohol.
What Are Some Example Calculations?
A 75 kg male who drank 3 standard drinks (each 14 g alcohol) over 2 hours: BAC = (42 / (75,000 * 0.68)) * 100 - (0.015 * 2) = 0.0824 - 0.03 = approximately 0.052%.
An 80 kg male consumes 2 standard drinks (US, 14 g each) over 1 hour.
Alcohol = 2 * 14 = 28 g. BAC = (28 / (80,000 * 0.68)) * 100 - (0.015 * 1) = (28 / 54,400) * 100 - 0.015 = 0.05147 - 0.015 = 0.0365%.
Estimated BAC: approximately 0.037%. Below most legal limits but impairment may still be present.
A 60 kg female consumes 3 glasses of wine (each 150 ml at 12%) over 2 hours.
Alcohol per glass = 150 * 0.12 * 0.789 = 14.2 g. Total = 3 * 14.2 = 42.6 g. BAC = (42.6 / (60,000 * 0.55)) * 100 - (0.015 * 2) = (42.6 / 33,000) * 100 - 0.03 = 0.1291 - 0.03 = 0.099%.
Estimated BAC: approximately 0.099%. Above the legal driving limit in most jurisdictions.
A 90 kg male consumed 4 beers (each 355 ml at 5%) and stopped drinking 3 hours ago.
Alcohol per beer = 355 * 0.05 * 0.789 = 14.0 g. Total = 4 * 14.0 = 56.0 g. BAC = (56.0 / (90,000 * 0.68)) * 100 - (0.015 * 3) = (56.0 / 61,200) * 100 - 0.045 = 0.0915 - 0.045 = 0.0465%.
Estimated BAC: approximately 0.047% after 3 hours. Still above zero and impairment may remain.
When Should You Use a BAC Calculator?
This calculator can be used for educational purposes to understand how alcohol affects your body and how long it takes to metabolise. It can help illustrate why "just a few drinks" may put you over the legal limit, especially for lighter individuals or women. It is also useful for understanding the concept of standard drinks and how different beverages compare in alcohol content.
However, this calculator must never be used as the sole basis for deciding whether to drive or perform any safety-sensitive activity. Individual variation in alcohol metabolism is significant — factors including genetics, food in the stomach, medications, liver health, fatigue, and tolerance all affect actual BAC. The estimates provided are mathematical approximations based on population averages and your actual BAC may be substantially higher or lower than calculated.
What Do These Terms Mean?
What Are the Best Tips to Know?
- Know your country's standard drink size (14 g in the US, 10 g in Australia/UK/EU, 8 g in some others) to count drinks accurately.
- Eating food before and during drinking slows alcohol absorption but does not reduce the total amount absorbed.
- The only thing that lowers BAC is time — coffee, cold showers, and exercise do not speed up alcohol metabolism.
- Alternate alcoholic drinks with water to slow your consumption rate and stay hydrated.
- Remember that BAC continues to rise for 30-60 minutes after your last drink as alcohol is still being absorbed.
What Mistakes Should You Avoid?
- Assuming you are safe to drive because your estimated BAC is below the legal limit — impairment begins well before the legal threshold.
- Not counting drinks accurately — a large pub pour of wine or a strong craft beer can contain 2-3 standard drinks.
- Believing that food, coffee, or time in cold air will sober you up faster — only time and liver metabolism reduce BAC.
- Forgetting that BAC peaks 30-60 minutes after your last drink, so you may be more impaired after stopping than while drinking.
Frequently Asked Questions
Can I use this calculator to decide if I am safe to drive?
No. This calculator provides rough estimates only. Individual variation is significant, and many factors (genetics, food, medications, fatigue) affect actual BAC. The only safe approach is to not drive after drinking, or to use a calibrated personal breathalyser for a more accurate reading.
What is the legal BAC limit for driving?
Legal limits vary by country: 0.08% in the US, England, and Wales; 0.05% in most of Europe, Australia, and many Asian countries; 0.03% in India and China; 0.02% in Sweden, Norway, and Poland; and 0.00% in some Middle Eastern and South Asian countries. Check your local laws.
How long does it take for one drink to leave my system?
On average, the body eliminates about one standard drink per hour (approximately 0.015% BAC per hour). However, this rate varies between individuals. A single standard drink may take 1-2 hours to fully metabolise.
Why does the same amount of alcohol affect women more than men?
Women typically have a higher body fat percentage and lower body water content than men of the same weight. Since alcohol distributes in body water, women achieve higher BAC levels per drink. Women also tend to have lower levels of alcohol dehydrogenase, an enzyme that breaks down alcohol in the stomach.
Does eating before drinking lower my BAC?
Eating slows the rate of alcohol absorption, which can reduce peak BAC, but it does not reduce the total amount of alcohol absorbed. Food in the stomach keeps the pyloric valve closed longer, slowing the passage of alcohol to the small intestine where most absorption occurs.
Why do I feel fine but the calculator says my BAC is high?
Tolerance to alcohol's subjective effects develops with regular drinking, but this does not reduce the actual impairment to reaction time, coordination, and judgement. Feeling fine is not a reliable indicator of BAC or impairment level.
How accurate is the Widmark formula?
The Widmark formula provides estimates within approximately 0.01-0.02% BAC for most people under controlled conditions. However, real-world accuracy varies due to individual differences in absorption rate, metabolism, body composition, hydration, and food intake. It should be treated as a rough guide, not a precise measurement.
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