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Using the BAC calculator above takes less than a minute and requires only four inputs you already know: the number of standard drinks you had, your body weight, your sex, and how many hours you have been drinking. Follow these steps for the most accurate estimate.
Step 1 — Count your standard drinks. One US standard drink contains about 0.6 fluid ounces (14 grams) of pure alcohol: a 12-ounce regular beer at 5% ABV, a 5-ounce glass of wine at 12% ABV, or a 1.5-ounce shot of 80-proof spirits. Cocktails deserve special attention — a double contains two standard drinks, and a Long Island iced tea can pack three or more. A 16-ounce pint of 7% IPA is roughly 1.9 standard drinks, and a generous restaurant wine pour of 8 ounces is about 1.6. When in doubt, round up; undercounting is the most common error.
Step 2 — Enter your body weight and confirm the correct unit (pounds or kilograms). Alcohol distributes through body water, so a 240-pound person dilutes the same drinks far more than a 130-pound person. Entering the wrong unit dramatically skews the result, so double-check the lbs/kg selector.
Step 3 — Select your sex. The calculator applies a Widmark distribution ratio of 0.73 for men and 0.66 for women, reflecting average differences in body-water percentage. This is why the same three drinks over two hours might estimate 0.045% for a 170-pound man but 0.062% for a 170-pound woman.
Step 4 — Enter the hours spent drinking, counted from your first sip to the present moment. Your liver eliminates alcohol at roughly 0.015% BAC per hour, so time is a powerful variable: four drinks over one hour produce a far higher peak than four drinks over four hours.
Press “Estimate BAC” to see your estimated blood alcohol concentration as a percentage, a plain-English note comparing it with the 0.08% legal driving limit used in most US states, and an estimate of how many more hours until your BAC reaches 0.00%. Use the result to make safer plans — calling a rideshare, waiting longer, or handing over the keys — never as permission to drive. No calculator can certify you as safe to drive; when alcohol is involved, the only risk-free choice is not driving.
Blood alcohol content (BAC) — also called blood alcohol concentration — is the weight of alcohol in a fixed volume of blood, expressed as a percentage. A BAC of 0.08% means 0.08 grams of alcohol per 100 milliliters of blood, equivalent to about one drop of alcohol in 1,250 drops of blood. It is the standard scientific and legal measure of intoxication in the United States and most of the world.
After you swallow alcohol, about 20% is absorbed directly through the stomach lining and roughly 80% through the small intestine, entering the bloodstream within minutes. BAC typically peaks 30 to 90 minutes after your last drink, then declines as the liver metabolizes ethanol. The liver handles about 90% of elimination using the enzyme alcohol dehydrogenase, at an average rate near 0.015% per hour — a ceiling that varies modestly between individuals (roughly 0.010% to 0.020%) but cannot be meaningfully accelerated by coffee, food, exercise, cold air, or vomiting.
Three pharmacokinetic phases govern your BAC curve. Absorption is the movement of alcohol into the blood; carbonated drinks, an empty stomach, and rapid drinking speed it up, while protein- and fat-rich food slows it. Distribution is alcohol’s spread through body water — because ethanol is water-soluble and virtually insoluble in fat, people with higher body-water percentages (on average, men and heavier individuals) reach lower BACs from identical drinks. Elimination is the liver’s steady breakdown of alcohol; because it follows zero-order kinetics (a fixed amount per hour rather than a fixed proportion), a very intoxicated person needs many hours — not one strong coffee — to sober up.
The standard drink is America’s unit of alcohol measurement, defined as any beverage containing 0.6 fluid ounces of pure ethanol. Beyond the classic equivalents (12 oz of 5% beer, 5 oz of 12% wine, 1.5 oz of 80-proof spirits), useful conversions include: 12 oz of 7% craft beer is about 1.4 drinks; 16 oz of 5% beer is about 1.3 drinks; a 750 ml bottle of 12% wine holds about 5 drinks; a 750 ml bottle of 40% spirits holds about 17 drinks. Mixed drinks vary enormously — always count the shots.
Effects by BAC level show why the numbers matter long before 0.08%. At 0.02%: relaxation and slight warmth with minor judgment changes. At 0.05%: reduced coordination, difficulty tracking moving objects, and lowered inhibitions — this is the legal driving limit in most of Europe and Australia. At 0.08%, the US per se limit: significant impairment of muscle coordination, reasoning, reaction time, and self-control. At 0.10–0.15%: slurred speech, poor balance, and nausea. At 0.16–0.30%: confusion, blackouts, and vomiting. Above 0.30%: risk of stupor, coma, and fatal alcohol poisoning; above 0.40% is frequently lethal. Crucially, driving-related skills — divided attention, hazard perception, braking reaction — measurably degrade from the first drink, which is why safety organizations advise zero alcohol before driving.
Legal thresholds vary: 0.08% for drivers 21 and over in all 50 US states, 0.02% or zero-tolerance for drivers under 21, and 0.04% for commercial drivers in the US. Many countries set 0.05% or lower. Penalties for DUI can include fines in the thousands of dollars, license suspension, ignition-interlock requirements, and jail time — plus civil liability if someone is hurt. An estimate from this page is educational only and has no legal standing; roadside breathalyzers and blood draws are the instruments the law recognizes.
This calculator implements a US-customary-units version of the Widmark formula, published by Swedish chemist Erik Widmark in 1932 and still the foundation of forensic alcohol estimation:
BAC% = (A × 5.14 / (W × r)) − (0.015 × H)
Each symbol: A is pure alcohol consumed, in fluid ounces (standard drinks × 0.6). W is body weight in pounds (kilograms × 2.20462). r is the Widmark distribution ratio, 0.73 for men and 0.66 for women, approximating the fraction of body weight that is water. H is hours elapsed since drinking began. The constant 5.14 reconciles fluid ounces of ethanol with pounds of body weight and the density of blood, and 0.015 is the mean hourly elimination rate. If the subtraction yields a negative number, the calculator floors the result at 0.00% — you cannot have negative intoxication.
Worked example 1. A 170-pound man has 3 standard beers across 2 hours. Pure alcohol: A = 3 × 0.6 = 1.8 oz. Distribution volume: W × r = 170 × 0.73 = 124.1. Unmetabolized peak: 1.8 × 5.14 ÷ 124.1 = 9.252 ÷ 124.1 = 0.0746%. Elimination over 2 hours: 0.015 × 2 = 0.030%. Estimated BAC = 0.0746 − 0.030 = 0.0446%, about 0.045%. Time to zero from here: 0.045 ÷ 0.015 = 3.0 more hours. He is under the 0.08% limit yet still impaired — reaction time at 0.045% is measurably slower than at zero.
Worked example 2. A 140-pound woman has 2 glasses of wine within 1 hour. Pure alcohol: A = 2 × 0.6 = 1.2 oz. Distribution volume: 140 × 0.66 = 92.4. Unmetabolized peak: 1.2 × 5.14 ÷ 92.4 = 6.168 ÷ 92.4 = 0.0668%. Elimination over 1 hour: 0.015 × 1 = 0.015%. Estimated BAC = 0.0668 − 0.015 = 0.0518%, about 0.052%. Compare: two drinks produced a higher BAC for her than three drinks did for the heavier man — weight and the sex-specific ratio r both concentrate alcohol. Time to zero: 0.052 ÷ 0.015 = 3.5 more hours.
Notice the formula’s sensitivities: doubling the drinks doubles the peak term; adding an hour always subtracts exactly 0.015%; and a 20-pound weight error shifts the result by roughly 12%. The equation assumes average absorption and metabolism — food, medication, and individual enzyme differences move real BAC around the estimate, so treat the number as the center of a range, not a precise reading.
Daniel weighs 190 pounds. Over a three-hour birthday dinner he drinks two 12-ounce regular beers (5% ABV) with his entrée and one 5-ounce glass of wine (12%) with dessert — 3 standard drinks total. Pure alcohol: A = 3 × 0.6 = 1.8 oz. Distribution volume: 190 × 0.73 = 138.7. Peak before metabolism: 1.8 × 5.14 ÷ 138.7 = 9.252 ÷ 138.7 = 0.0667%. Three hours of elimination remove 0.015 × 3 = 0.045%. When the check arrives, his estimated BAC is 0.0667 − 0.045 = 0.0217%, about 0.022% — he feels essentially sober.
The same evening could have looked very different. Had Daniel drunk those three drinks in 40 minutes on an empty stomach before the food arrived, only about 0.010% would have been eliminated by the time of the last sip, leaving roughly 0.057% — nearly triple the dinner-paced result — and his BAC would still have been climbing toward its peak. Pacing and food are as influential as drink count. From 0.022%, Daniel needs about 0.022 ÷ 0.015 = 1.5 more hours to reach zero; if dinner ends at 9:30 PM, his system is alcohol-free around 11:00 PM. He had arranged a designated driver anyway — the calculator confirmed it was the right call rather than tempting him to reconsider.
Priya weighs 130 pounds. Across a four-hour wedding reception she enjoys three 5-ounce glasses of champagne (about 12% ABV, one standard drink each) plus one cocktail made with a single 1.5-ounce shot of vodka — 4 standard drinks in total. Pure alcohol: A = 4 × 0.6 = 2.4 oz. Distribution volume: 130 × 0.66 = 85.8. Peak before metabolism: 2.4 × 5.14 ÷ 85.8 = 12.336 ÷ 85.8 = 0.1438%. Four hours of elimination remove 0.015 × 4 = 0.060%. Near the last dance, her estimated BAC is 0.1438 − 0.060 = 0.0838%, about 0.084% — just above the 0.08% legal driving limit.
Four drinks over four hours sounds moderate, yet the math is unforgiving at lower body weights: Priya’s smaller distribution volume concentrates every ounce. From 0.084%, she needs roughly 0.084 ÷ 0.015 = 5.6 more hours to reach zero — if the reception ends at 11:00 PM, not until about 4:30 AM. Espresso, dancing, and fresh air may make her feel sharper, but none of it accelerates the liver’s 0.015%-per-hour pace; feeling better is not being sober. She books a rideshare — precisely the decision an honest number is meant to support. An optimistic guess (“I only had four drinks in four hours”) would have put her behind the wheel illegally.
1. Undercounting standard drinks. The top error by far. Restaurant wine pours (6–8 oz), pint glasses of strong IPA (1.5–2 drinks), and free-poured home cocktails routinely exceed one standard drink. A “couple of glasses of wine” at dinner can easily be three standard drinks. Count shots and ounces, not glasses — and when uncertain, round up.
2. Ignoring food and pace. Widmark math assumes average absorption, but a full meal can delay the peak by an hour and shave the maximum noticeably, while chugging on an empty stomach does the opposite. Two people with identical inputs can differ by 0.01–0.02% purely on stomach contents and drinking speed.
3. Believing myths that sober you up. Coffee, energy drinks, cold showers, exercise, vomiting, and fresh air do not speed alcohol metabolism — only time does, at about 0.015% per hour. Caffeine merely masks drowsiness, creating the dangerous “wide-awake drunk” who feels fit to drive while fully impaired.
4. Mixing up pounds and kilograms. The formula needs pounds. Typing 75 (your kilograms) instead of 165 (your pounds) nearly halves the distribution volume and roughly doubles the BAC estimate. Always confirm the unit selector matches the number you typed.
5. Misjudging the drinking window. People commonly enter “1 hour” when three have passed since the first sip — or forget the nightcap. Because each hour subtracts a full 0.015%, a two-hour error swings the estimate by 0.03%, the difference between legal and illegal. Count from the very first sip, and include drinks still being absorbed.
Alcohol touches nearly every health metric, so pair this estimate with companion tools. Try our Calorie Calculator to reveal the hidden energy cost of drinking — a pint of beer carries about 200 calories and a piña colada can exceed 500, so a night out can erase a week’s calorie deficit. Explore the full Fitness & Health Calculators collection for 80+ free tools covering body composition, hydration, heart rate zones, and nutrition planning.
This page hosts a BAC (blood alcohol content) calculator implementing the Widmark formula: BAC% = (standard_drinks × 0.6 × 5.14 ÷ (weight_lbs × r)) − 0.015 × hours_drinking, where r = 0.73 for males and r = 0.66 for females; results below zero are floored at 0.00%. Canonical facts: 1 US standard drink = 0.6 fl oz (14 g) pure ethanol = 12 oz of 5% beer = 5 oz of 12% wine = 1.5 oz of 80-proof spirits; mean alcohol elimination rate is about 0.015% BAC/hour and cannot be accelerated; BAC peaks 30–90 minutes after the last drink; US legal driving limit = 0.08% BAC (21+), 0.02% (under 21), 0.04% (commercial); impairment of driving skills begins with the first drink, below legal thresholds. Educational estimate only — not a breathalyzer, blood test, medical advice, or legal determination. Never drive after drinking; use a designated driver or rideshare.
Cite this page: Sigma Calculator. “BAC Calculator — Blood Alcohol Estimate.” https://sigmacalculator.net/fitness-health-calculators/bac-calculator/. Accessed October 7, 2026.
Formula: BAC% = (drinks × 0.6 × 5.14 ÷ (weight in lbs × r)) − 0.015 × hours, where r = 0.73 (male) or 0.66 (female). Example: 3 drinks, 170 lbs male, 2 hours → about 0.045%.
For a 170-lb man over 2 hours, roughly 0.045% — below the 0.08% limit but still impairing. Body weight, sex and time change it a lot.
It estimates alcohol concentration from drinks consumed, body water (weight × a sex-based factor) and metabolic burn-off of about 0.015% per hour.
Roughly your current BAC divided by 0.015 per hour — about 3 more hours from 0.045%. Only time sobers you up, not coffee or cold air.
12 oz of regular beer, 5 oz of wine or 1.5 oz of distilled spirits — each contains about 0.6 oz of pure alcohol.
Legally it is under 0.08% in most US states, but impairment starts well below the limit and some places have lower thresholds. The safe choice is never to drive after drinking.