BAC Calculator – Blood Alcohol Concentration
Estimate your Blood Alcohol Concentration (BAC) based on drinks, weight, and time.
How Blood Alcohol Concentration (BAC) Works
Blood Alcohol Concentration (BAC) measures the percentage of alcohol in your bloodstream. A BAC of 0.08% — the legal driving limit in most US states and many countries — means 0.08 grams of alcohol per 100 mL of blood.
Alcohol is absorbed through the stomach and small intestine, peaks in the blood 30–90 minutes after drinking, and is eliminated at roughly 0.015% per hour — about one standard drink per hour.
Widmark Formula: How BAC is Estimated
The Widmark formula is the most common BAC estimation method: BAC = (alcohol grams / (weight × r)) × 100 − (elimination rate × hours). The "r" factor is 0.68 for men and 0.55 for women, reflecting differences in body water distribution. Women typically reach higher BAC levels than men of the same weight after identical alcohol consumption.
A 70 kg man who drinks 3 standard drinks (36g alcohol) in 2 hours would have approximately: (36 / (70000 × 0.68)) × 100 − (0.015 × 2) ≈ 0.046%.
BAC Effects by Level
0.02–0.05%: Mild relaxation, slight impairment of judgment
0.05–0.08%: Reduced coordination, slower reaction time
0.08–0.15%: Significant impairment — illegal to drive
0.15–0.30%: Severe disorientation, nausea, blackout risk
0.30%+: Medical emergency, risk of coma or death
This calculator estimates BAC only. Never use an estimated BAC to decide whether to drive.
Frequently Asked Questions
How long until I am sober?
Your body eliminates alcohol at roughly 0.015% BAC per hour. Divide your BAC by 0.015 to estimate hours until sober. Coffee, cold showers, and food do not speed this up.
What counts as one standard drink?
In the US: 12 oz regular beer (5%), 5 oz wine (12%), or 1.5 oz spirits (40%). Each contains roughly 14g of pure alcohol.
Why do women reach higher BAC?
Women generally have a higher body fat percentage and lower body water ratio, plus lower levels of the enzyme alcohol dehydrogenase. Both factors mean alcohol is less diluted and metabolized more slowly.