BAC Calculator
Estimate your blood alcohol content based on drinks, body weight, and time elapsed
Your weight affects how alcohol is distributed in your body
How long ago you started drinking — used to calculate metabolism
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Estimate Your Blood Alcohol Content
Enter your details and drinks above to see your estimated BAC, impairment level, time to sober, and projected BAC timeline.
How to Use the BAC Calculator
Enter Your Physical Details
Select your gender (male or female) and enter your body weight in pounds or kilograms. Gender determines the Widmark distribution factor used in the calculation, and weight affects how alcohol is diluted across your body mass. These two inputs have the greatest impact on your BAC estimate.
Add Your Drinks
Click Add Drink to log each beverage you consumed. Select the drink type (beer, wine, spirits, or cocktail), choose a preset or enter a custom size in ounces, and set the ABV (alcohol by volume) percentage. Add multiple entries if you had different types of drinks. Use the cocktail presets for popular mixed drinks with pre-filled ABV values.
Set Time and Conditions
Enter the total time since your first drink in hours and minutes. Select your stomach contents level: empty stomach means full alcohol absorption, a light meal reduces peak BAC by about 25%, and a full meal can reduce it by up to 50%. Optionally adjust the metabolism rate slider if you know your body processes alcohol faster or slower than average.
Review Your Results
Click Calculate BAC to see your estimated blood alcohol content, impairment level with effects description, time until your BAC returns to zero, peak BAC reached during the session, and a visual timeline showing your projected BAC decline. Compare your result against your country's legal driving limit. Use the export or print buttons to save your results.
Frequently Asked Questions
How does the BAC calculator work?
This calculator uses the Widmark formula, the most widely accepted scientific method for estimating blood alcohol content. The formula takes the total grams of pure alcohol you consumed (calculated from drink volumes and ABV percentages), divides it by your body weight multiplied by a gender-specific distribution constant (0.68 for males, 0.55 for females), then subtracts the alcohol your body has metabolized over time at a rate of approximately 0.015% per hour. The result is your estimated BAC as a percentage. The calculator also factors in stomach contents, which affect absorption rate. A full meal can reduce peak BAC by up to 50% compared to drinking on an empty stomach. While the Widmark formula is reliable for most people, individual results may vary based on genetics, medications, and health factors.
What is the legal BAC limit for driving?
Legal BAC limits vary by country and driver type. In the United States, the legal limit is 0.08% for adult drivers (21 and over), 0.04% for commercial vehicle operators, and effectively 0.00% to 0.02% for drivers under 21 (zero-tolerance laws). The United Kingdom and Canada also use 0.08%, while Australia and Germany set a stricter limit of 0.05%. Japan enforces 0.03%, and Sweden has one of the world's lowest limits at 0.02%. It is important to understand that impairment begins at BAC levels well below the legal threshold. Research shows reduced visual function and divided attention at just 0.02%. The legal limit represents the enforcement threshold, not a safe level for driving.
How long does it take for alcohol to leave your system?
Your body metabolizes alcohol at a roughly constant rate of 0.010% to 0.020% BAC per hour, with the average being about 0.015% per hour. This means if your BAC is 0.08%, it would take approximately 5 hours and 20 minutes to return to 0.00%. At 0.15% BAC, you would need roughly 10 hours. Nothing can speed up this process — not coffee, cold showers, food, or exercise. These may make you feel more alert, but they do not reduce your BAC. Your liver processes alcohol at a fixed rate determined by your enzyme levels. The only factor that truly reduces BAC is time. Sleep does not speed up metabolism either, but it gives your body the time it needs to process the remaining alcohol.
Does eating food affect your BAC?
Yes, food has a significant effect on your BAC. Eating before or while drinking slows the rate at which alcohol is absorbed into your bloodstream by delaying gastric emptying — the process by which stomach contents pass into the small intestine where most alcohol absorption occurs. Drinking on an empty stomach allows alcohol to reach the small intestine quickly, producing a higher and faster peak BAC. A light meal or snack can reduce peak BAC by approximately 25%, while a substantial meal (especially one containing fats, proteins, and carbohydrates) can reduce peak BAC by up to 50%. However, food only slows absorption; it does not prevent it. The same total amount of alcohol will eventually be absorbed regardless of food intake. The benefit is a lower, more gradual peak that gives your liver more time to metabolize the alcohol.
How accurate is this BAC calculator?
BAC calculators using the Widmark formula provide reasonable estimates for most people but are not precise to the level of a blood test or calibrated breathalyzer. The formula is based on population averages for body water content and metabolism rates, which can vary significantly between individuals. Factors like genetics, liver health, medications (including common ones like aspirin and antacids), hydration level, and chronic alcohol use patterns all influence actual BAC but are not captured by the formula. Studies suggest the Widmark method is typically accurate within plus or minus 0.01% to 0.02% for moderate drinkers. For safety-critical decisions like driving, always treat the estimate as approximate and err on the side of caution. This calculator is an educational tool, not a substitute for a certified breathalyzer or medical assessment.