BAC Calculator
Estimate your blood alcohol content from the number of drinks, your weight, sex, and hours since your first drink — and see how long until you're back to zero.
1 standard drink = 12 oz beer (5%), 5 oz wine (12%), or 1.5 oz spirits (40%) — about 14 g of alcohol.
Estimates only — never drive after drinking. Real BAC varies with food, medications, health, and individual metabolism. This tool cannot tell you whether you are safe or legal to drive.
Enter your weight, drinks, and hours to estimate BAC.
Estimated BAC
—
—
Under 0.08% in
—
US legal driving limit
Back to zero in
—
at 0.015%/hour
BAC hour by hour
| Time from now | Estimated BAC | Status |
|---|
How it works
How blood alcohol content is estimated.
- 01
Count the alcohol, not the drinks
Every US standard drink contains roughly 14 grams of pure alcohol, whether it's a 12 oz beer at 5% ABV, a 5 oz glass of wine at 12%, or a 1.5 oz shot of 40% spirits. The calculator multiplies your drink count by 14 g to get total alcohol consumed. Stronger pours count as more than one standard drink — a 9% IPA in a pint glass is closer to 2 standard drinks than 1.
- 02
Apply the Widmark formula
BAC% = (alcohol grams ÷ (body weight in grams × r)) × 100. The Widmark ratio r accounts for body water: about 0.68 for men and 0.55 for women, which is why the same drinks produce a higher BAC in women and lighter people. This peak value assumes the alcohol is fully absorbed — absorption itself takes 30–90 minutes, longer on a full stomach.
- 03
Subtract elimination over time
The liver clears alcohol at a nearly constant ~0.015% BAC per hour — about one standard drink per hour — regardless of coffee, water, or exercise. The calculator subtracts 0.015 × hours since your first drink, then projects forward hour by hour until you reach 0.00%. Because elimination is linear, a high BAC takes many hours to clear: 0.15% needs about 10 hours.
FAQ
Frequently asked questions.
How do you calculate blood alcohol content (BAC)?
BAC is estimated with the Widmark formula: BAC% = (alcohol in grams ÷ (body weight in grams × r)) × 100 − (0.015 × hours since drinking started). The distribution ratio r is about 0.68 for men and 0.55 for women, because bodies differ in water content. One US standard drink contains about 14 grams of pure alcohol. Example: a 180 lb man who had 4 standard drinks over 2 hours has an estimated BAC of about 0.071%.
How many drinks does it take to reach 0.08% BAC?
It varies with weight, sex, and timing. Roughly: a 180 lb man reaches ~0.08% after about 4 standard drinks in 2 hours, while a 140 lb woman can pass 0.08% with just 2–3 drinks in the same window. Food, medications, fatigue, and individual metabolism all shift the real number, so treat any estimate as approximate — the only safe driving BAC is 0.00%.
How long until my BAC is back to zero?
The body eliminates alcohol at a nearly constant rate of about 0.015% BAC per hour — roughly one standard drink per hour. Divide your current BAC by 0.015 to estimate the hours to zero. A BAC of 0.10% takes about 6 hours 40 minutes to fully clear. Coffee, cold showers, and exercise do not speed this up; only time lowers BAC.
What does 0.08 BAC mean in mg per 100 ml?
A BAC of 0.08% equals 80 mg of alcohol per 100 mL of blood (0.08 grams per deciliter). BAC is a percentage by mass: for every 100 mL of blood there are 0.08 grams of alcohol. 0.08% is the legal driving limit in most US states; Utah uses 0.05%, and many countries set 0.05% or lower.
How dangerous is a BAC of 0.30% or higher?
A BAC of 0.30–0.40% usually means alcohol poisoning — a life-threatening emergency with possible loss of consciousness, vomiting, and dangerously slowed breathing. Above 0.40%, coma and death from respiratory arrest become likely. If someone shows signs of alcohol poisoning (unresponsive, slow or irregular breathing, cold clammy skin), call emergency services immediately.
Related
Related calculators.
Last updated: July 28, 2026