BAC Calculator (Blood Alcohol Content)

Estimate your blood alcohol content (BAC) using the Widmark formula.

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Enter your values and click Calculate

This BAC calculator uses the Widmark formula to estimate your blood alcohol concentration based on the number of standard drinks consumed, your body weight, the time elapsed since you started drinking, and your biological sex. A standard drink in the United States contains 14 grams of pure alcohol — equivalent to a 12 oz regular beer (5% ABV), a 5 oz glass of wine (12% ABV), or a 1.5 oz shot of 80-proof spirits. The results are estimates only. Actual BAC is affected by many factors this calculator cannot account for: food consumption, individual metabolism, medications, hydration, body composition, and drinking pace. This tool is for educational purposes. Never use a BAC estimate to decide whether it is safe to drive. The legal limit for driving in all US states is 0.08% BAC, but impairment begins well below that threshold — even at 0.02–0.05% BAC, reaction time and judgment are measurably affected.

How It Works

This calculator uses the Widmark formula: BAC = (drinks × 14 × 5.14) ÷ (weight in lbs × r) − (0.015 × hours). Each standard drink contains 14 grams of alcohol. The constant 5.14 converts grams per pound into the percentage unit used for BAC. The Widmark factor r (also called the volume of distribution) accounts for the fact that alcohol distributes throughout body water — r is 0.73 for biological males and 0.66 for biological females, reflecting differences in average body water content and body composition. The elimination term (0.015 × hours) accounts for the liver metabolizing approximately 0.015% BAC per hour on average. Important: actual metabolism rates vary from 0.010% to 0.030% per hour depending on the individual. Food, medications, hydration, and drinking pace all affect real-world BAC. Never drive after drinking — impairment begins well below the legal 0.08% limit.

Examples

Two Beers in One Hour
A 160 lb male who drank 2 standard drinks over 1 hour.
Result: Estimated BAC ≈ 0.047% — Buzzed (mild effects).
Four Drinks at a Party
A 130 lb female who had 4 drinks over 2 hours.
Result: Estimated BAC ≈ 0.098% — Drunk (over the legal limit).
Morning After Check
A 180 lb male checking BAC 8 hours after having 5 drinks.
Result: Estimated BAC ≈ 0.020% — near zero, but marginal impairment may remain.

Frequently Asked Questions

What counts as one standard drink?
In the United States, one standard drink contains 14 grams of pure alcohol. This equals: a 12 oz regular beer at 5% ABV, a 5 oz glass of wine at 12% ABV, or a 1.5 oz shot of 80-proof (40% ABV) spirits. Many craft beers (7–10% ABV), large wine pours, and cocktails made with multiple spirits count as 1.5–2+ standard drinks. Using the actual alcohol content of what you're drinking will give a more accurate result.
Can I use this to decide if I'm safe to drive?
No. This calculator provides an estimate based on average physiological parameters and should never be used to determine driving safety. Individual BAC varies significantly based on factors this calculator cannot measure: food consumption, drinking pace, body fat percentage, liver function, medications, and hydration. The only reliable way to know your BAC is a certified breathalyzer or blood test. Even at BAC levels below 0.08%, driving ability is impaired. If you have consumed alcohol, the safest choice is not to drive.
Why does biological sex affect BAC?
Biological females typically have a higher percentage of body fat and lower percentage of body water than biological males of the same weight. Since alcohol distributes through body water (not fat), the same amount of alcohol becomes more concentrated in a female's system. This is captured in the Widmark r factor: 0.73 for males and 0.66 for females. Hormonal fluctuations can also affect alcohol metabolism, particularly around the menstrual cycle.
How long does it take for BAC to reach zero?
The liver eliminates alcohol at a rate of approximately 0.015% BAC per hour on average, though this varies from 0.010% to 0.030% per person. There is no way to speed up this process — coffee, water, food, and cold showers do not accelerate alcohol metabolism. They may make you feel more alert but do not lower your BAC. Time is the only remedy. Divide your estimated BAC by 0.015 to get a rough estimate of hours until sober.

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