Blood Alcohol Concentration (BAC) Calculator

Q: Why is this BAC calculator only an estimate?

This Blood Alcohol Content calculator provides an estimate because it uses population averages for key variables. Your personal BAC can be affected by your genetics (ADH/ALDH enzymes), metabolism rate, chronic alcohol use, how quickly you drank, whether you have eaten recently, medications, fatigue, and overall health.

Q: What is a standard drink?

In the United States, a standard drink contains approximately 14 grams (0.6 fl oz) of pure alcohol. This corresponds to a 12 oz beer (5% ABV), a 5 oz glass of wine (12% ABV), or a 1.5 oz shot of distilled spirits (40% ABV).

Q: Why are there different factors for males and females?

The Widmark formula uses different constants because of average differences in body composition. On average, females have a higher percentage of body fat and a lower percentage of body water than males of the same weight. Since alcohol distributes in body water, the same amount of alcohol will lead to a higher concentration in a female's body. These are population averages, and individual distribution volume varies.

Q: Is a BAC below 0.08 safe to drive?

No. A BAC under 0.08 g/dL is not 'safe.' Measurable impairment of judgment, coordination, and reaction time begins at around 0.02, and crash risk rises across the entire range below the legal limit. The 0.08 limit is the threshold for the offense of driving while impaired in most U.S. states (0.05 in Utah, 0.04 for commercial drivers, and zero-tolerance for drivers under 21), not a safety guarantee.

Biological Sex

Weight Unit

Weight

—

Drinks Consumed

Light Beer (12 oz / 355 mL, 4.2%)

Beer (12 oz / 355 mL, 5%)

IPA Beer (16 oz / 473 mL, 6.5%)

Wine (5 oz / 148 mL, 13%)

Cocktail (4 oz / 118 mL, 30%)

Liquor (1.5 oz / 44 mL, 40%)

Time Since Last Drink

Estimated BAC

0.000%

Est. Time Until Sober

—

(Estimate only. Do NOT use to decide if it’s safe to drive)

0.00 0.05 (Impaired) 0.08 (Illegal) 0.12+

Show your work

This calculator uses the Widmark equation to estimate Blood Alcohol Content:

BAC (%) = [ Alcohol (g) ÷ ( Body weight (g) × r ) ] × 100 − ( Hours × β )

Step 1 — Grams of pure alcohol per drink: Volume (mL) × ABV (fraction) × 0.789 g/mL (density of ethanol). Each drink’s grams are summed.

Step 2 — Peak BAC: Total alcohol grams ÷ ( body weight in grams × r ), then × 100. The Widmark factor r reflects the body-water fraction (≈ 0.68 for males, ≈ 0.55 for females).

Step 3 — Subtract elimination: Hours since the last drink × β, where β is the elimination rate (≈ 0.015 % per hour). The result is floored at 0.

Time until sober: Current BAC ÷ β (≈ 0.015 % per hour).

This is a reference for how the estimate is produced. Constants (r, β, ethanol density) are population averages and vary between individuals.

Recent Updates

Jun 2026 — Clarified that a BAC below 0.08 g/dL is not “safe”: measurable impairment and increased crash risk begin from around 0.02.
Jun 2026 — Added a rising-BAC caveat (alcohol can still be absorbing, with peak around 30–90 minutes and delayed by food), so a low estimate can understate current BAC.
Jun 2026 — Noted that the elimination rate (β ≈ 0.015 %/hr) varies between people, so “Time Until Sober” can be substantially wrong and must never be used to decide whether to drive.

Jones AW. Evidence-based survey of the elimination rates of ethanol from blood with applications in forensic casework. Forensic Sci Int. 2010;200(1-3):1-20. PMID 20304569. · National Highway Traffic Safety Administration. Drunk Driving. Retrieved 2026.

Key Information

This Blood Alcohol Content calculator provides an estimate only and has no legal standing. Do not use it to determine if it is safe to drive.
A reading below 0.08 is not “safe.” Measurable impairment and increased crash risk are present from about 0.02.
Legal limits in the U.S.: 0.08 g/dL in 49 states and DC, 0.05 in Utah, 0.04 for commercial drivers, and zero-tolerance (typically 0.00–0.02) for drivers under 21.
Alcohol may still be absorbing after your last drink (peak around 30–90 minutes, later with food), so a low or “sober” estimate can understate your current BAC.
Alcohol is eliminated at roughly 0.015% per hour on average, but this varies between people; only time lowers your BAC.
If you drink, do not drive. Plan for a designated driver or use a ride-sharing service.

About This Blood Alcohol Content Calculator

This Blood Alcohol Content Calculator estimates your BAC using the widely recognized Widmark formula. It is intended for educational and informational purposes only. The calculation is based on your biological sex, body weight, the quantity of alcohol consumed, and the time that has passed since your last drink. While this tool can provide a helpful estimate, it cannot account for all individual physiological factors. Never rely on this Blood Alcohol Content calculator to make decisions about driving.

The Formula Explained

The Widmark formula is a common method for estimating BAC. It works by calculating the concentration of alcohol in the body’s total water content and then subtracting the amount of alcohol that has been metabolized over time.

$$ \text{BAC %} = \left( \frac{\text{Alcohol (g)}}{\text{Body Weight (g)} \times r} \right) \times 100 – (\text{Hours} \times 0.015) $$

Alcohol (g): The total mass of pure alcohol consumed (volume × ABV × 0.789 g/mL, the density of ethanol).
Body Weight (g): Your weight converted to grams.
r (Widmark Factor): The volume of distribution / body-water ratio, approximately 0.55 for females and 0.68 for males on average.
0.015 (β): The average elimination rate in % per hour. Reported values typically range from about 0.01 to 0.025 %/hr.

Both r and the elimination rate β are population averages. Independent forensic reviews report meaningful between-person variation in each, which is why any single calculated BAC carries inherent uncertainty.

Why a Result Below 0.08 Is Not “Safe”

The 0.08 g/dL figure is the legal threshold for the per se offense of impaired driving in most U.S. states — it is not a line below which driving is safe. Laboratory and epidemiological data show that judgment, divided attention, reaction time, and coordination are measurably impaired from around 0.02, and relative crash risk rises continuously across the sub-legal range. Treat any positive estimate as a reason not to drive.

0.08 g/dL — legal limit in 49 states and the District of Columbia (drivers 21+).
0.05 g/dL — legal limit in Utah.
0.04 g/dL — limit for commercial drivers.
0.00–0.02 g/dL — zero-tolerance limits for drivers under 21.

Rising BAC: Your Estimate Can Be Too Low

Alcohol is absorbed over time, not instantly. After your last drink, blood alcohol typically continues to rise and peaks around 30–90 minutes later, and food in the stomach delays that peak further. Because of this, a “sober” or low estimate shortly after drinking can understate your true current BAC — you may actually be more impaired than the number suggests. This tool models elimination but cannot reliably model your individual absorption curve.

Elimination Rate Variability: “Time Until Sober” Is Only a Guess

The “Time Until Sober” estimate divides your current BAC by a single average elimination rate of 0.015% per hour. In reality, β varies substantially between individuals — for example, chronic heavy drinkers often eliminate alcohol faster than occasional drinkers, and reported rates span roughly 0.01–0.025 %/hr. As a result, the time shown here can be substantially wrong in either direction. Never use it to decide when it is safe to drive.

Limitations

This Blood Alcohol Content calculator provides an estimate, not a legally-admissible measurement. The calculation does not account for many individual factors that can influence BAC, including:

Genetics: Variation in alcohol-metabolizing enzymes (ADH and ALDH) alters how quickly alcohol is processed.
Chronic alcohol use: Regular heavy drinking can increase the elimination rate, while liver disease can decrease it.
Drinking speed: Drinking quickly produces a higher, earlier peak than the same amount spread over time.
Food consumption: Eating before or during drinking slows absorption and delays the peak.
Biological sex and body composition: Body-water fraction and fat mass affect alcohol distribution.
Medications: Certain drugs interact with alcohol and affect its absorption or metabolism.
Overall health: Liver function and general health status alter alcohol processing.

Due to these variables, the calculated BAC should be considered a rough guide only. Never use this tool to determine if you are fit to drive or operate machinery.

Frequently Asked Questions (FAQ)

1. Why is this BAC calculator only an estimate?

This Blood Alcohol Content calculator provides an estimate because it uses population averages for key variables. Your personal BAC can be affected by your genetics (ADH/ALDH enzymes), metabolism rate, chronic alcohol use, how quickly you drank, whether you’ve eaten recently (food slows alcohol absorption), medications, fatigue, and overall health.

2. How does eating food affect my BAC?

Eating food, especially before drinking, slows the absorption of alcohol from the stomach into the bloodstream. This typically results in a lower peak BAC than drinking on an empty stomach, but the total amount of alcohol absorbed remains the same. Food also delays the time to peak BAC, so your blood alcohol may still be rising for longer after your last drink.

3. What is a “standard drink”?

In the United States, a “standard drink” contains approximately 14 grams (0.6 fl oz) of pure alcohol. This corresponds to a 12 oz beer (5% ABV), a 5 oz glass of wine (12% ABV), or a 1.5 oz shot of distilled spirits (40% ABV).

4. Can I get sober faster?

No. The only thing that lowers your BAC is time. The liver metabolizes alcohol at a roughly constant rate. Coffee, cold showers, or exercise may make you feel more alert, but they do not speed up alcohol elimination or improve your level of impairment.

5. Why are there different factors for males and females?

The Widmark formula used by this Blood Alcohol Content calculator uses different constants because of average differences in body composition. On average, females have a higher percentage of body fat and a lower percentage of body water than males of the same weight. Since alcohol distributes in body water, the same amount of alcohol will lead to a higher concentration in a female’s body. These are population averages, and individual distribution volume varies.

6. Is a BAC below 0.08 safe to drive?

No. A BAC under 0.08 g/dL is not “safe.” Measurable impairment of judgment, coordination, and reaction time begins at around 0.02, and crash risk rises across the entire range below the legal limit. The 0.08 limit (0.05 in Utah, 0.04 for commercial drivers, zero-tolerance for drivers under 21) is the legal threshold for an offense, not a safety guarantee.

📖 Sources:

Widmark, E. M. P. (1932). Principles and applications of medicolegal alcohol determination. Berlin: Urban & Schwarzenberg.
Jones AW. Evidence-based survey of the elimination rates of ethanol from blood with applications in forensic casework. Forensic Sci Int. 2010;200(1-3):1-20. PMID: 20304569.
Maskell PD, Jones AW, Savage A, Scott-Ham M. Evidence based survey of the distribution volume of ethanol. Forensic Sci Int. 2019;294:124-131. PMID: 30553124.
Maskell PD, Speers RA, Maskell DL. Improving uncertainty in Widmark equation calculations: alcohol volume, strength and density. Sci Justice. 2017;57(5):321-330. PMID: 28889860.
National Highway Traffic Safety Administration (NHTSA). Drunk Driving. Retrieved from nhtsa.gov.
National Institute on Alcohol Abuse and Alcoholism (NIAAA). What Is A Standard Drink?. Retrieved from niaaa.nih.gov.

⚠️ Disclaimer:

This tool provides an estimate for informational purposes only and has no legal standing. It is not a substitute for professional medical or legal advice. A result below any legal limit does not mean you are unimpaired or safe to drive. NEVER drink and drive. Relying on this Blood Alcohol Content calculator to determine your fitness to drive could result in serious harm, death, or legal consequences. If you or someone you know needs help with alcohol use, contact the SAMHSA National Helpline at 1-800-662-HELP (4357).

Blood Alcohol Content Calculator

🍻 Blood Alcohol Content (BAC) Calculator