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Blood Alcohol Concentration (BAC) Calculator

Estimate your blood alcohol concentration, see how alcohol affects the body, and find out roughly how long it may take for your BAC to return to zero.

hours

minutes

Amount of Alcohol Consumed

Beer

Wine

Liquor

Other / Custom drink

Tip: leave a drink row blank if you didn't have it. Use "Other" for cocktails or drinks not listed.

What Is BAC?

Blood Alcohol Concentration (BAC) is the percentage of alcohol present in your bloodstream, expressed as grams of ethanol per 100 millilitres of blood. A BAC of 0.08% — the legal driving limit in most of the United States — means there are 0.08 grams of alcohol per 100 mL of blood.

Unlike most other measurements of intoxication, BAC is the legal and clinical standard for measuring alcohol impairment. It is used by law enforcement, hospitals, and researchers because, unlike subjective measures, it can be directly tested via breath, blood, urine, or saliva.

This calculator uses the Widmark formula — the same method developed by Swedish chemist Erik Widmark in the 1930s — to give a rough estimate of BAC. It is intended for education only. It cannot replace a breathalyser or blood test, and no online tool can ever tell you whether you are safe to drive.

How BAC Is Calculated — The Widmark Formula

Widmark Equation

BAC % = (A / (W × r)) × 100 − β × t

A — alcohol consumed in grams

W — body weight in grams

r — Widmark distribution ratio (0.68 male, 0.55 female)

β — elimination rate ≈ 0.015% / hour

t — hours since first drink

Step 1: convert each drink to grams of pure ethanol using volume (mL) × ABV% × 0.789. Step 2: sum the grams of alcohol. Step 3: divide by your body water volume (weight × r × 10) to get peak BAC. Step 4: subtract 0.015% for every hour since you started drinking to estimate current BAC.

How to Use This BAC Calculator

#1

Understand a past evening

Plug in what you drank to see roughly how your BAC tracked over the night and when it likely returned to zero.

#2

Compare drink sizes

See how a pint of strong craft beer can deliver more alcohol than a glass of wine, and why ABV matters more than drink count.

#3

Learn impairment thresholds

Visualise where 0.02%, 0.05%, and 0.08% fall on your personal BAC curve — and how legal limits compare to actual impairment.

BAC and Impairment Levels

Effects vary by individual, tolerance, and circumstances. Source: NHTSA and NIAAA.

BAC RangeTypical Effects
0.00 – 0.02%Minimal effects; subtle changes possible in mood. Driving skill can still drop measurably.
0.02 – 0.05%Relaxed feeling. Mild changes in reaction time and divided attention. Crash risk roughly doubles vs. 0.00.
0.05 – 0.08%Loss of small-muscle control, judgment, alertness. Crash risk ~4× higher. Legal driving limit in many countries.
0.08 – 0.15%US legal limit (0.08). Major loss of coordination, balance, reaction. Slurred speech and memory impairment likely.
0.15 – 0.30%Severe impairment. Loss of balance, vomiting, possible blackouts. High risk of injury.
0.30+%Loss of consciousness, risk of coma. 0.40%+ can be fatal — seek emergency medical care.

Factors That Affect BAC

BAC is determined by more than just the number of drinks. Each of the following can shift your real BAC well above or below any calculator estimate.

Biological sex

Women typically reach a higher BAC than men of the same weight after the same drinks due to less body water and lower levels of alcohol dehydrogenase.

Body weight & composition

Higher body water = more dilution. Lean mass holds more water than fat mass, so muscular people often reach lower BAC than less-lean people of the same total weight.

Drinking speed

Drinking quickly raises peak BAC because the liver can only metabolise ~0.015% per hour. Spacing drinks out lowers the peak.

Food in stomach

Food slows absorption — especially fat and protein — which lowers peak BAC for the same drinks. Drinking on an empty stomach raises peak BAC by ~20–25%.

Hydration

Dehydration concentrates alcohol in the blood. Water doesn't speed elimination but supports overall recovery and reduces hangover severity.

Medications

Many prescription drugs (sedatives, painkillers, antidepressants, antibiotics) interact with alcohol and can dramatically change its effects on the brain and liver.

Age

Older adults reach higher BACs from the same drinks because body water decreases with age. Liver enzyme activity may also decline.

Genetics

Genetic variants in alcohol dehydrogenase and aldehyde dehydrogenase produce wide variation in how quickly people metabolise alcohol — from very fast to very slow.

Why BAC Estimates Are Not Exact

The Widmark formula assumes a single, average distribution ratio for each sex and a fixed elimination rate. In reality both vary substantially between people, and even within the same person on different days.

Independent studies have shown that BAC predictions can deviate from real blood tests by up to ±30–40%. Two people drinking the same amount in the same time can land at very different real BACs — one over the legal limit, one below — even when this calculator gives them the same number.

Treat the result here as a teaching tool to understand how drinking patterns map to impairment ranges — not as a verdict on whether you are safe to drive, operate machinery, or make a decision that depends on sobriety.

BAC Legal Limits Around the World

LimitExamples
0.00%Czech Republic, Hungary, Romania, Saudi Arabia, UAE (zero tolerance)
0.02%Norway, Sweden, Poland, Estonia; US (under 21, zero-tolerance variant)
0.03%India, Japan, China
0.04%United States (commercial drivers, all states)
0.05%Australia, Germany, France, Italy, Spain, UK (Scotland), Utah (US)
0.08%United States (most states, drivers 21+), Canada, UK (England & Wales), New Zealand

Penalties and the exact threshold vary by jurisdiction and driver category (young, novice, commercial). Always check your local law.

Common BAC Myths

✗ Myth: Coffee sobers you up.

✓ Fact: Caffeine makes you feel more alert but does not lower BAC. A 'wide-awake drunk' is still impaired and remains a danger behind the wheel.

✗ Myth: A cold shower will sober you up.

✓ Fact: Cold water has zero effect on BAC. It may briefly raise alertness, masking the real degree of impairment.

✗ Myth: Eating after drinking lowers BAC quickly.

✓ Fact: Food only slows absorption of alcohol still in your stomach. Alcohol already in your blood is processed by the liver at a fixed rate.

✗ Myth: Beer is safer than spirits.

✓ Fact: It's the total grams of ethanol that determine BAC, not the form. A pint of strong beer can contain more alcohol than a shot of vodka.

✗ Myth: Tolerance lowers BAC.

✓ Fact: High tolerance changes how impaired you feel, not how much alcohol is in your blood. Tolerant drinkers can still register high BACs and be legally over the limit.

What Counts as a Standard Drink?

In the United States, one "standard drink" contains about 14 grams (0.6 fl oz) of pure ethanol. The serving size depends on ABV.

Regular beer

12 oz / 355 ml

~5% ABV

Malt liquor

8–9 oz / 240–265 ml

~7% ABV

Wine

5 oz / 148 ml

~12% ABV

Distilled spirits

1.5 oz / 44 ml

~40% ABV

Source: NIAAA — What Is A Standard Drink?

Frequently Asked Questions

Common questions about blood alcohol concentration, the Widmark formula, and alcohol impairment.

Blood Alcohol Concentration (BAC) is the percentage of alcohol in your bloodstream, expressed as grams of ethanol per 100 millilitres of blood. A BAC of 0.08% means 0.08 grams of alcohol per 100 mL of blood. It depends on how much you drank, how fast, your body weight, biological sex, body composition, food intake, and individual metabolism.

BAC calculators give a rough estimate based on the Widmark formula and population averages. Actual BAC can vary by 30–40% from any prediction because it depends on stomach contents, hydration, medications, genetics, body fat percentage, drinking speed, and individual liver enzyme activity. The result is educational only — never use it to decide whether you are safe to drive.

In all 50 US states the legal driving limit is 0.08% BAC for drivers 21+ (Utah uses 0.05%). For commercial drivers it is 0.04%, and zero-tolerance laws apply to drivers under 21. Measurable impairment, however, starts at 0.02–0.04% BAC according to the NHTSA — legal limits are not safety thresholds.

Healthy adults eliminate alcohol at roughly 0.015% BAC per hour — the body cannot speed this up. A peak BAC of 0.08% takes about 5–6 hours to return to zero, and 0.15% takes about 10 hours. Breath, urine, and saliva tests can detect alcohol for up to 24 hours; hair tests can detect heavy use for up to 90 days.

Food in your stomach slows alcohol absorption, which lowers the peak BAC for the same amount consumed — but it does not change the total amount of alcohol your body has to process. A high-protein, high-fat meal is most effective at slowing absorption. Drinking on an empty stomach can produce a BAC roughly 20–25% higher.

Yes. The volume of total body water is the main factor that determines how much your body dilutes a given amount of alcohol. A heavier person generally reaches a lower BAC from the same drink than a lighter person. The Widmark formula models this with a distribution ratio (~0.68 for men, ~0.55 for women) applied to body weight.

Yes. Women on average have a higher body fat percentage and lower body water percentage than men, so alcohol distributes into a smaller volume. Women also produce less of the stomach enzyme alcohol dehydrogenase, which means more alcohol reaches the bloodstream intact. These differences are reflected in lower Widmark distribution ratios for women.

No. Driving impairment begins at BAC levels far below 0.08%. The NHTSA reports measurable declines in tracking and divided attention from 0.02% BAC, and significant impairment of judgment by 0.05%. The only safe BAC for driving is 0.00%. This calculator is for education only and must not be used to decide whether to drive.

Most adults eliminate alcohol at roughly 0.015% BAC per hour — about one standard US drink (14 g of ethanol) per hour. This rate cannot be sped up by coffee, energy drinks, water, exercise, or sleep. Heavy drinkers may metabolise slightly faster, while people with liver disease eliminate alcohol more slowly.

Developed by Swedish chemist Erik Widmark in the 1930s, the basic form is BAC% = (A / (W × r)) × 100 − β × t, where A is grams of alcohol consumed, W is body weight in grams, r is the distribution ratio (~0.68 men, ~0.55 women), β is the elimination rate (~0.015% per hour), and t is hours since the first drink.

About This Page

Methodology

Widmark formula

BAC is estimated using the classic Widmark equation with a 0.789 g/mL ethanol density, sex-specific distribution ratios (0.68 male, 0.55 female), and a 0.015% / hour elimination rate sourced from CDC/NIAAA-reported population averages.

Editorial

SamCalculator Editorial Team

Content is researched against US public-health sources — NIAAA, CDC, and NHTSA — and clearly labels every estimate as educational. We never frame the result as a green light to drive.

References

  1. 1.National Institute on Alcohol Abuse and Alcoholism (NIAAA). Alcohol Facts and Statistics. https://www.niaaa.nih.gov/alcohols-effects-health/alcohol-topics/alcohol-facts-and-statistics
  2. 2.Centers for Disease Control and Prevention (CDC). Alcohol Use and Your Health. https://www.cdc.gov/alcohol/data-stats.htm
  3. 3.National Highway Traffic Safety Administration (NHTSA). Drunk Driving. https://www.nhtsa.gov/risky-driving/drunk-driving
  4. 4.Jones AW. Disposition and fate of ethanol in the body. Forensic Sci Rev. 2010. https://pubmed.ncbi.nlm.nih.gov/26271115/
  5. 5.Widmark EMP. Principles and applications of medicolegal alcohol determination. 1932. https://pubmed.ncbi.nlm.nih.gov/8889727/
  6. 6.NIAAA — What Is a Standard Drink? https://www.niaaa.nih.gov/alcohol-health/overview-alcohol-consumption/what-standard-drink

Educational Disclaimer

The BAC value produced by this calculator is an estimate generated by a formula. Real blood alcohol concentration depends on food, hydration, medication, body composition, hormones, sleep, genetics, and many other factors that no online tool can know about. Predictions can be off by 30–40% in either direction.

Do not use the result here to decide whether you are safe to drive, operate machinery, or make legal or medical decisions. If you are concerned about alcohol use — yours or someone else's — talk to a healthcare provider or contact the SAMHSA National Helpline (1-800-662-4357) in the United States. The only safe BAC for driving is 0.00%.

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