Health Tool
BAC Calculator
Estimate your Blood Alcohol Concentration from a session drink log or a single drink, using the Widmark formula that forensic toxicologists use. The log keeps its running standard-drink count on this device, so a refresh mid-evening does not lose your night, and the projected curve shows exactly when you cross back under the 0.08% limit.
BAC Estimator
Step 1 — What you drank
Add each round to the session log to mix drink types, or leave the log empty and estimate straight from the drink selected here.
1.0 standard drinks per serving
How many servings of the selected drink
Session log
0.0 standard drinks · 0.0 g alcohol · 0 entries
Nothing logged yet. Estimating now uses the drink selected above; add drinks to mix types across the evening and keep the total after a refresh.
Step 2 — About you
Body water is what alcohol distributes into, so weight and sex drive the estimate as strongly as the drink count does.
Weight in pounds
Determines the body water ratio used in the Widmark formula
How to Use This BAC Calculator
Log the round
Pick one of 18 preset drinks or enter your own volume and ABV, set the servings, and add it to the session log. The log survives a refresh, so you can keep adding across the evening.
Describe yourself
Body weight in pounds or kilograms, biological sex for the Widmark body-water factor, and how long ago the first drink was poured.
Read the curve
You get current and peak BAC, the impairment band, the half-hourly decay curve with the 0.08% marker drawn on it, and the time until you are under the limit and at zero.
Worked examples
Two Sessions, Step by Step
Three beers, 160 lb man, one hour in
One 12 oz beer at 5% ABV is 12 x 29.5735 = 354.9 ml of liquid, of which 5% is 17.74 ml of ethanol, which at 0.789 g/ml weighs 14.0 g — exactly one US standard drink. Three of them is 42.0 g.
A 160 lb body is 72,575 g, and the male Widmark factor of 0.68 gives 49,351 g of distribution volume. So peak BAC is 42.0 / 49,351 x 100 = 0.085%. Subtract one hour of elimination at 0.015 and the estimate now is 0.070% — under the 0.08% limit, but squarely in the moderate impairment band, and zero is still 4h 40min away.
Six beers, 180 lb man, two hours in
Six standard drinks is 84.0 g of ethanol. A 180 lb body is 81,647 g, times 0.68 is 55,520 g, so peak BAC is 84.0 / 55,520 x 100 = 0.151%.
Two hours of elimination removes 0.030, leaving 0.121% now: significant impairment, and roughly one and a half times the legal limit. Getting back under 0.08% takes another 2h 45min, and reaching zero takes 8h 5min. Two extra beers cost five and a half extra hours.
Per-se thresholds
US Legal BAC Limits
The commonly repeated claim that 0.08% is the limit in all 50 states has been wrong since the end of 2018, when Utah moved to 0.05%. The 0.08% figure is correct for 49 states and the District of Columbia. Note also that every one of these numbers is a per-se threshold: it is the point at which the reading alone establishes the offence. Below it you can still be arrested and convicted for driving while impaired if an officer and a prosecutor can show impairment by other evidence.
Standard Limit
The per-se limit for drivers 21 and older: at or above it you are guilty of DUI on the number alone, with no further proof of impairment required.
49 states and D.C. (every state except Utah)
Lower Limit States
Utah cut its general DUI threshold to 0.05% on 30 December 2018, the lowest in the country. It is the reason the 0.08% figure is not nationwide.
Utah only
Commercial Drivers
Half the standard limit, set federally for holders of a commercial driver license while operating a commercial motor vehicle.
Federal standard, all states
Under 21 (Zero Tolerance)
Every state enforces a zero-tolerance law for drivers under 21. Most set the threshold at 0.00% or 0.01%; some allow up to 0.02%.
All 50 states and D.C.
What the number means
Impairment at Each BAC Band
Impairment is continuous, not a switch that flips at the legal limit. NHTSA crash data shows measurable degradation of divided-attention tasks and steering control from about 0.02%, well below any per-se threshold, and relative crash risk roughly doubles for each 0.02 percentage points added above 0.05%. The bands below describe typical effects; a light drinker will feel each band sooner than a heavy one, but the crash statistics do not care about tolerance.
Sober / Minimal Effect
Little to no impairment. Normal behavior expected.
Mild Impairment
Relaxation, slight euphoria. Judgment and inhibitions begin to decrease. Reaction time may slow.
Moderate Impairment
Reduced coordination, impaired peripheral vision and reaction time. Over the per-se limit in 49 states and D.C. from 0.08%.
Significant Impairment
Poor muscle control, possible nausea, major loss of judgment and self-control. Do not drive under any circumstances.
Dangerous Level
Risk of loss of consciousness, memory blackout, respiratory depression, and alcohol poisoning. Seek medical attention.
Methodology
Widmark Formula Details
BAC = (A / (W x r)) x 100 - (0.015 x t)Each drink is first converted into grams of pure alcohol:
A (grams) = volume (oz) x 29.5735 (ml/oz) x ABV x 0.789 (g/ml density)Then the Widmark variables are:
- A = total grams of pure alcohol consumed
- W = body weight in grams (lbs x 453.592)
- r = Widmark factor: 0.68 for males, 0.55 for females
- t = hours since the first drink
- 0.015 = average metabolic elimination rate, in BAC percentage points per hour
The Widmark factor is a body-water fraction, not a fudge factor. Alcohol distributes into water and not into fat or bone, and the average male body is about 68% water by weight against about 55% for females. A smaller distribution volume concentrates the same dose, which is why identical drinks produce a higher reading in a woman than in a man of the same weight.
The 0.015 elimination rate is a population average for social drinkers. Individual rates run from roughly 0.010 to 0.020 percentage points per hour depending on genetics, liver health and chronic exposure; heavy drinkers metabolise faster because of enzyme induction, which lowers their BAC curve without lowering their crash risk.
Known limitations
What This Estimate Cannot See
Absorption. The model has no absorption phase: it credits your bloodstream with every gram at hour zero. In reality ethanol takes roughly 30 to 90 minutes to cross from the stomach and small intestine into the blood, and food slows that further. The first hour of the curve therefore reads high, and your real peak arrives later and is flatter than the chart.
Food. A substantial meal before drinking can lower peak BAC by roughly 25 to 50% for the same dose, because the pyloric sphincter holds alcohol in the stomach where absorption is slow. It does not reduce the total alcohol absorbed, so it flattens the peak without shortening the time to zero.
Body composition. Weight is a poor proxy for body water. Two people at 180 lb with different muscle-to-fat ratios can differ by 15% or more in distribution volume, and that error passes straight through to the BAC figure. Widmark r values published in forensic literature range from about 0.60 to 0.75 for men and 0.50 to 0.62 for women.
Medication and health. Liver disease, some antibiotics, antihistamines, opioids and benzodiazepines all interact with alcohol, either by changing metabolism or by adding their own impairment on top of it. Impairment can be severe at a BAC this calculator would describe as mild.
Drinking pace. The formula uses only the total dose and the elapsed time, so six drinks in one hour and six drinks over five hours produce the same peak figure. In the body they do not: the fast session overwhelms the elimination rate and reaches a much higher real peak.
Frequently Asked Questions
What BAC level is legally drunk in the US?
In 49 states plus D.C., the per-se DUI limit for drivers 21 and older is 0.08% BAC. Utah is the exception at 0.05%, a threshold it adopted on 30 December 2018. Commercial drivers face a 0.04% federal limit while operating a commercial vehicle, and every state enforces a zero-tolerance law between 0.00% and 0.02% for drivers under 21. Per se means the number alone convicts: no field sobriety evidence is needed. You can also be charged below any of these numbers if an officer judges you impaired.
What is the Widmark formula?
The Widmark formula, BAC = A / (W x r) x 100 - beta x t, was published by Swedish physician Erik Widmark in 1932 and is still the basis of forensic BAC estimation. A is the total grams of pure alcohol consumed, W is body weight in grams, r is the Widmark factor for body-water fraction (0.68 for men, 0.55 for women), beta is the elimination rate of roughly 0.015 BAC percentage points per hour, and t is the hours since the first drink. This calculator runs exactly that equation and shows every input it used.
Does this calculator account for the time it takes alcohol to absorb?
No, and that is the single largest simplification in the model. Widmark treats every gram of alcohol as if it entered your bloodstream the moment the session began, whereas real absorption from the stomach and small intestine takes roughly 30 to 90 minutes, longer on a full stomach. The practical effect is that the first hour of the curve reads too high and your true peak arrives later and lower than the chart shows. On the way down, past about 90 minutes after your last drink, the estimate tracks reality more closely.
How accurate is a BAC calculator?
It is an estimate with a wide error band, not a measurement. The Widmark factor r varies between individuals by roughly plus or minus 15% because body composition differs at the same weight, and the elimination rate ranges from about 0.010 to 0.020 percentage points per hour depending on genetics, liver health and drinking history. Food, medication, hydration and how fast you drank move the answer further. The only ways to know your real BAC are a calibrated evidential breath test or a blood draw. Never use a calculator to decide whether you are safe to drive.
How long does it take to sober up?
Your body clears alcohol at roughly 0.015 BAC percentage points per hour, and that rate barely responds to anything you do. One US standard drink, 14 grams of pure alcohol, takes about one to one and a half hours to clear. Coffee, cold showers, exercise, water and food do not accelerate hepatic alcohol metabolism; they only make you a more alert drunk. Starting from 0.15% you need about ten hours to reach zero, which is why the morning-after drive is a common way to be arrested.
What counts as one standard drink?
A US standard drink is 14 grams (0.6 fl oz) of pure alcohol, the definition used by the NIAAA and the CDC. That is 12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% spirits: all three land on 14 grams by design. Real servings often do not. A 16 oz pour of 7% IPA is 1.9 standard drinks, a 9 oz restaurant pour of 14% wine is 2.1, and a Long Island iced tea is closer to 3. The session log on this page converts each drink for you, which is why its running total is usually higher than the number of glasses you remember.
Why does the same drink give a woman a higher BAC than a man?
Because the alcohol distributes into body water, not body mass, and the average female body carries a smaller water fraction at the same weight. That is what the Widmark r factor captures: 0.55 for women against 0.68 for men. At 160 lb, three standard drinks put a man at about 0.085% and a woman at about 0.105%, a 24% difference from identical drinks. Lower average levels of gastric alcohol dehydrogenase, the enzyme that breaks down some alcohol before it reaches the bloodstream, widen the gap further.
Authoritative Sources
- NHTSA - Drunk Driving
Federal position on the 0.08% per-se limit, zero-tolerance laws for drivers under 21, and the 0.04% commercial threshold.
- CDC - Alcohol Use and Your Health
Standard drink definition of 14 grams of pure alcohol and the 12 oz beer / 5 oz wine / 1.5 oz spirits equivalences used throughout this page.
- NIAAA - What Is a Standard Drink?
Source for the 0.6 fl oz (14 g) standard drink and the ABV-based conversion this calculator applies to each preset.
- Utah Code 41-6a-502 - Driving under the influence
Statutory text setting Utah at 0.05%, effective 30 December 2018 - the reason 0.08% is not a 50-state figure.
- NIAAA - Alcohol Metabolism and Elimination
Elimination-rate range of roughly 0.010 to 0.020 BAC percentage points per hour and the absorption timing behind the caveat above.
Disclaimer
Not medical or legal advice, and not evidence of sobriety. This page runs a population-average model on the numbers you type in; it cannot see your stomach contents, your medication, your liver or how fast you drank, and the plausible error on any single estimate is wide enough to cross a legal threshold in either direction. The only authoritative readings are a calibrated evidential breath test or a blood draw. If you have been drinking, do not drive. All calculations run locally in your browser and the session log stays on this device; nothing is uploaded.
Published by Kalcify · Last updated
Calculators are built against primary sources — government tax authorities (IRS, HMRC, CRA, ATO) for finance and the World Health Organization for health metrics. Updated when rates or rules change. View methodology and data sources.
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