BAC Calculator

Blood alcohol concentration, or BAC, is the weight of alcohol in a set volume of blood. In the United States it is written as a percentage: a BAC of 0.08% means 0.08 grams of alcohol in every 100 milliliters of blood, which is the same as 0.08 g/dL or 80 mg/dL. The number climbs while alcohol is absorbed from your stomach and small intestine, then falls at a roughly steady pace as your liver breaks it down.

This blood alcohol calculator answers two questions: roughly where your BAC is now, and how long it will take to fall to 0.08 and then to zero. It cannot measure anything. Only a breath test or a blood test measures alcohol, and even those are snapshots of a level that is still moving.

The Widmark formula

Swedish physician Erik Widmark published the dilution model behind almost every BAC estimate in 1932, and forensic toxicologists still use it today. It divides the alcohol you drank by the share of your body it spreads through, then subtracts what your liver has removed:

The factor r is the Widmark distribution ratio. Alcohol dissolves in water, not fat, so r describes how much of your body weight behaves like blood water. The second term is elimination: 0.015 g/dL per hour is a widely used population average. In practical terms, one standard drink raises the estimate by about 0.025 for a 180 lb man and by about 0.040 for a 140 lb woman before any time has passed.

Worked example: a 180 lb man, four beers, two hours

Four 12 oz beers at 5% alcohol are four standard drinks, or 4 × 14 = 56 grams of alcohol. His body weight is 180 × 453.59 = 81,647 grams, and multiplying by r = 0.68 gives 55,520 grams of effective body water.

His estimated BAC is 0.071%. That is under the 0.08 limit, yet already over Utah's 0.05 limit and the 0.04 federal limit for commercial drivers. Without another drink he reaches 0.05 in 1 h 24 min, 0.04 in 2 h 4 min and zero in 4 h 44 min. The hour-by-hour path is 0.071, 0.056, 0.041, 0.026, 0.011 and then 0.000. These are exactly the values the calculator shows with its default settings.

Worked example: a 140 lb woman, three glasses of wine

Three 5 oz glasses of 12% wine are three standard drinks, or 42 grams of alcohol. Her body weight is 63,503 grams, and with r = 0.55 the effective body water is 34,927 grams. The peak works out to 42 ÷ 34,927 × 100 = 0.120. After 1.5 hours she has eliminated 0.0225, which leaves an estimated 0.098%.

She drops to 0.08 in 1 h 12 min, to 0.05 in 3 h 12 min and to zero in 6 h 32 min. Compare that with the first example: she drank one drink fewer than the man, over a shorter time, and still lands higher and stays elevated nearly two hours longer. Lower body weight and a lower Widmark factor both push in the same direction.

What counts as a standard drink

The National Institute on Alcohol Abuse and Alcoholism (NIAAA) defines a US standard drink as any drink containing 0.6 fl oz, or 14 grams, of pure alcohol. That is 12 oz of regular beer at about 5%, 8 to 10 oz of malt liquor at about 7%, 5 oz of table wine at about 12%, or a 1.5 oz shot of 80-proof spirits at 40%.

Real drinks rarely match those sizes. The calculator converts any custom drink with a simple rule: fluid ounces × percent ABV ÷ 60 = standard drinks. A 16 oz craft IPA at 7% is 1.87 standard drinks, a 16 oz pint of 5% lager is 1.33, a generous 9 oz pour of 13.5% wine is 2.03 and a 25 oz can at 8% is 3.33. Counting glasses instead of standard drinks is the fastest way to underestimate your BAC.

BAC one hour after drinking, by weight and number of drinks

These tables apply the same formula the calculator uses: standard drinks of 14 g, one hour since the first drink, and 0.015 eliminated. Values at or above 0.080 are shown in red. Read across your weight row to see how quickly each extra drink adds up.

Two patterns stand out. A 120 lb woman crosses 0.08 between her second and third drink, while a 240 lb man reaches it at his fifth. And before any elimination, a woman's estimate is 24% higher than a man's at the same weight, the ratio 0.68 ÷ 0.55 = 1.24. Once an hour of elimination is subtracted, the relative gap in the tables grows further: 0.110 against 0.086 at 180 lb and four drinks.

How long does it take to sober up?

Once drinking stops and absorption is finished, the time to reach zero is simply your BAC divided by your elimination rate. The calculator uses 0.015 per hour. A review of controlled studies by A. W. Jones found 0.010 to 0.015 per hour after drinking on an empty stomach and 0.015 to 0.020 after a meal, with 0.015 a good average for moderate drinkers. The table shows how much that personal rate matters.

The same arithmetic exposes the popular "one drink per hour" rule. In the Widmark model, a 180 lb man clears about 8.3 grams of alcohol an hour, roughly 0.6 of a standard drink, and a 140 lb woman about 5.2 grams, closer to 0.4 of a drink. Pacing yourself at one drink an hour still lets BAC climb for most people.

Legal limits in the United States

• 0.08 for adult drivers. NHTSA states that driving at 0.08 or higher is illegal in all 50 states, the District of Columbia and Puerto Rico, with one exception.
• 0.05 in Utah. Utah's lower limit took effect on December 30, 2018, the first in the country.
• 0.04 for commercial drivers. Federal rule 49 CFR 382.201 bars CDL holders from safety-sensitive work at 0.04 or higher, and under 382.505 a test between 0.02 and 0.039 still takes a driver off duty for at least 24 hours.
• Zero tolerance under 21. According to NHTSA, every state sets a limit of 0.02 or lower for drivers under 21, and some use 0.00.

NHTSA's own guide adds that a driver can be arrested below 0.08 when an officer has probable cause based on driving behavior. The agency also estimates that a driver at 0.08 is about four times as likely to crash as a sober driver, and a driver at 0.15 at least twelve times as likely.

What changes your BAC

• Body weight. More body water dilutes the same alcohol. After three drinks in an hour, a 100 lb man is estimated at 0.121, more than twice the 0.053 of a 200 lb man.
• Sex. NHTSA notes that women generally have less water and more fat per pound, so more alcohol stays in the blood. The model uses r = 0.55 instead of 0.68.
• Pace. Alcohol drunk quickly arrives faster than the liver can clear it. Four drinks in one hour leave a 180 lb man at 0.086; the same four drinks spread over two hours leave 0.071.
• Food. A meal slows absorption, flattens the peak and is linked with faster elimination. The Widmark estimate does not include this, so it tends to overstate the peak after a large meal.
• Body composition. Two people at 180 lb can differ in body water. A lean, muscular person usually has a higher r than the average and a lower BAC.
• Medications. NHTSA points out that medications do not change your BAC, but some make you more impaired at the same level. Ask a pharmacist about yours.

How to use this calculator

1. Choose your sex. It selects the Widmark factor, 0.68 or 0.55.
2. Enter your current weight in pounds, or switch to kilograms.
3. Enter the hours since your first drink, not your last. Use decimals for part hours.
4. Build your drinks. Tap plus for each beer, glass of wine or shot. For anything else, enter the size in fluid ounces and the ABV printed on the label, then add as many as you had.
5. Read the result. The headline is the estimate now. The tiles show the wait until 0.08 and until zero, your total in standard drinks and the peak before elimination. Below are your status against each legal limit, an hour-by-hour table and NHTSA's typical effects.

Who this calculator is for

It is for anyone who wants to understand how drinks turn into blood alcohol: people planning when to stop drinking before an early start, hosts deciding how much to serve, students in health and driver education classes, and anyone curious why the same night out hits two people differently. It is also useful the morning after, when alcohol from a long night can still be in the blood. It is not for deciding whether to drive, for legal defense or for medical decisions.

Key terms

• BAC: grams of alcohol per 100 mL of blood, written as a percentage.
• Standard drink: 14 g (0.6 fl oz) of pure alcohol in the US.
• ABV: alcohol by volume, the percentage printed on the label. Proof is twice the ABV.
• Widmark factor (r): the share of body weight alcohol spreads through, about 0.68 for men and 0.55 for women.
• Elimination rate: how fast BAC falls once absorption is done, 0.015 per hour on average.
• Per se limit: a BAC at which driving is illegal on its own, without other proof of impairment.
• Binge drinking: NIAAA's term for a pattern that brings BAC to 0.08, typically five or more drinks for men or four or more for women in about two hours.

Limitations of any BAC estimate

The Widmark model makes three simplifications. It treats all alcohol as absorbed at once, while NHTSA notes that alcohol can be measured in the blood within 30 to 70 minutes after a drink, so a recent drink is still on its way in. It uses a single average r for each sex, while one German study measured body-water ratios from 0.60 to 0.87 in men and 0.44 to 0.80 in women. And it applies one fixed elimination rate, while real rates run from about 0.010 to 0.035 per hour, the top end seen in heavy drinkers whose livers have adapted.

Put together, those uncertainties are large. An error-propagation analysis by R. G. Gullberg found a standard uncertainty of 0.0255 for a calculated BAC of 0.120, a coefficient of variation of about 21%. A different person with your exact inputs could reasonably measure several hundredths higher or lower. That is why the honest use of this tool is planning and learning, and why it should never stand in for a breathalyzer or for simply not driving.

Related calculators

• The 2025 blood pressure guideline lists drinking less alcohol among its lifestyle steps. Check where your readings fall with the Blood Pressure Calculator.
• To see how much weight you carry around your middle, use the Waist to Height Ratio Calculator.
• To add a waiting time to the current clock time, use the Hours Calculator or the Time Calculator.
• To convert milliliters on an imported bottle into fluid ounces, use the Unit Converter.
• For daily energy needs, including what drinks add, use the Calorie Calculator.

Sources

• National Institute on Alcohol Abuse and Alcoholism (NIAAA, NIH), What Is A Standard Drink? (14 g, 0.6 fl oz; beer, malt liquor, wine and spirits sizes).
• NIAAA, Understanding the Dangers of Alcohol Overdose (BAC can rise after drinking stops; coffee and cold showers do not reverse effects; binge drinking definition), updated December 2025.
• National Highway Traffic Safety Administration (NHTSA), Drunk Driving (0.08 limit, Utah exception, crash risk).
• NHTSA, The ABCs of BAC, DOT HS 809 844 (typical effects by BAC, absorption within 30 to 70 minutes, arrests below 0.08).
• NHTSA, Countermeasures That Work: Lower BAC Limits (Utah 0.05 from December 30, 2018) and Zero-Tolerance Law Enforcement (under-21 limits).
• Federal Motor Carrier Safety Regulations, 49 CFR Part 382, sections 382.201 and 382.505 (commercial drivers).
• Jones AW (2010), "Evidence-based survey of the elimination rates of ethanol from blood with applications in forensic casework," Forensic Science International, PubMed.
• Li YC, Sze NN, Wong SC, et al. (2019), breath alcohol study stating average Widmark factors of 0.68 for males and 0.55 for females, PLoS One, PubMed.
• Seidl S, Jensen U, Alt A (2000), "The calculation of blood ethanol concentrations in males and females," International Journal of Legal Medicine, PubMed.
• Gullberg RG (2007), "Estimating the uncertainty associated with Widmark's equation as commonly applied in forensic toxicology," Forensic Science International, PubMed.
• Widmark EMP (1932), Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung, the original description of the formula.