BAC Calculator

BAC is calculated using the Widmark formula: BAC = (grams of alcohol consumed / (body weight in grams × Widmark factor r)) × 100, minus (elimination rate × hours drinking). The Widmark factor r represents body water ratio: 0.73 for men, 0.66 for women. The standard elimination rate is approximately 0.015% per hour. For example: a 160 lb (72.5 kg) man who drinks 2 standard drinks (28g alcohol) over 2 hours has a BAC of approximately: (28 / (72,500 × 0.73)) × 100 − (0.015 × 2) = 0.053% − 0.03% = 0.023%.

In the United States, the federal legal limit is 0.08% BAC for drivers 21 and older in all 50 states. Utah has a stricter limit of 0.05%. For commercial drivers (CDL holders), the limit is 0.04%. For drivers under 21, most states enforce zero-tolerance laws with limits of 0.00-0.02%. In many other countries, the limit is 0.05% (most of Europe, Australia, Canada). Some countries enforce 0.00% (Czech Republic, Hungary, Japan). Remember that impairment begins well before 0.08% — even at 0.04%, reaction time and judgment are measurably affected.

BAC drops at approximately 0.015% per hour through liver metabolism. This rate is relatively constant regardless of coffee, exercise, cold showers, or other interventions. Examples: starting BAC of 0.08% takes about 5.3 hours to reach 0.00%. Starting BAC of 0.15% takes about 10 hours. Starting BAC of 0.25% takes about 17 hours. Individual variation exists based on liver health and genetics, but these estimates are reasonably accurate for most healthy adults. Sleep does not accelerate alcohol metabolism — a person who passes out with a BAC of 0.20% will still have a significant BAC in the morning.

Women typically reach higher BAC for three reasons: lower body water percentage (alcohol distributes in body water, so less water means higher concentration), lower levels of alcohol dehydrogenase enzyme in the stomach (less first-pass metabolism before alcohol enters bloodstream), and typically lower body weight. The Widmark factor r is 0.73 for men and 0.66 for women, reflecting the body water difference. Body composition also matters within each sex — a lean, muscular man has more body water than an overweight man of the same weight, resulting in lower BAC for the same intake.

Yes, but only absorption speed, not elimination. Eating before or while drinking significantly slows alcohol absorption from the stomach into the bloodstream. This reduces peak BAC and delays when peak BAC is reached. A full stomach can reduce peak BAC by 30-50% compared to drinking on an empty stomach. However, the total amount of alcohol processed by the liver is the same — food does not make you sober faster, it only reduces how high your BAC gets. Fatty and protein-rich foods slow absorption most effectively. Eating after drinking is almost ineffective since alcohol is already in the bloodstream.

No. This calculator provides estimates with significant uncertainty margins. Individual variation in alcohol metabolism, absorption, and tolerance means actual BAC can differ from calculated BAC by 20-30% or more. Additionally, impairment for driving begins below 0.08% — at 0.05-0.06%, reaction time, divided attention, and lane tracking are already measurably impaired. You can be charged with driving while impaired even below 0.08% if an officer observes impaired driving. The only safe approach is zero alcohol before driving. Use a rideshare, taxi, or designated driver.

In the United States, one standard drink contains 14 grams (0.6 fl oz) of pure alcohol. This equals: 12 oz regular beer (5% ABV), 8-9 oz malt liquor (7% ABV), 5 oz table wine (12% ABV), 3-4 oz fortified wine such as port or sherry (17% ABV), 1.5 oz (one shot) of 80-proof spirits (40% ABV). Note that many common drinks exceed one standard drink: a pint (16 oz) of 7% craft beer is 1.9 standard drinks; a 750 ml bottle of 13% wine is 5 standard drinks; a large cocktail with 3 oz of spirits is 2 standard drinks. Serving sizes at bars are often larger than standard drink definitions.

Tolerance affects how you feel at a given BAC, not the actual BAC itself. A person with high alcohol tolerance may feel minimal impairment at 0.10% BAC, but their reaction time, coordination, and driving ability are just as impaired as someone who feels very drunk at the same level. This is why experienced drinkers who "don't feel drunk" are still dangerous drivers at elevated BAC — and why they may underestimate their impairment. Long-term heavy drinking does cause metabolic tolerance (the liver becomes slightly more efficient at metabolizing alcohol), but this effect is modest (10-20% faster elimination at most) and does not make high BAC levels safe.

Sleep does not accelerate alcohol metabolism. BAC continues to drop at the same 0.015% per hour rate whether awake or asleep. This is why "sleeping it off" requires genuinely adequate time. If someone goes to sleep at midnight with a BAC of 0.15%, they will still have a BAC of 0.075% (just below the legal limit) at 7 AM — seven hours later. At 9 AM they would be at 0.045%, still above zero. Morning-after driving with residual alcohol is a real and underappreciated risk. A useful rule: if you drank heavily the night before, do not drive until you have allowed sufficient metabolism time based on your estimated peak BAC.

BAC calculators have significant inherent uncertainty. The Widmark formula estimates have a reported accuracy of plus or minus 20-30% compared to measured BAC in studies. Key sources of variation: uncertainty in exact drink volumes and ABV, individual differences in alcohol absorption rate, body composition differences within each sex (lean vs. fat at the same weight), liver health and enzyme levels, genetics (ADH enzyme variants), medications that interact with alcohol metabolism, and stomach contents. Breathalyzers used by law enforcement have their own error margins (typically plus or minus 10%), which is why blood tests are used as legal confirmation. Never rely on any calculator to determine driving safety.