Blood Alcohol (BAC)
Estimated blood alcohol content by the Widmark formula.
Estimated BAC
0.050%
Under US legal limit (0.08)
Standard drinks
3
Hours elapsed
2
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How the Blood Alcohol (BAC) works
This Blood Alcohol Content (BAC) calculator estimates your current blood alcohol level using the scientifically validated Widmark formula, based on your weight, sex, the number and type of drinks consumed, and the time elapsed since you started drinking. It's designed for anyone who wants a data-informed sense of their impairment level before making decisions about driving, operating machinery, or other safety-sensitive activities.
The calculator uses the Widmark formula, developed by Swedish pharmacologist Erik Widmark in the 1930s and still the gold standard for BAC estimation. The core calculation divides the total grams of pure alcohol consumed by your body weight multiplied by a sex-specific distribution constant (r), then subtracts the alcohol metabolized over time at a standard elimination rate. This gives you a percentage representing how many grams of alcohol are present per 100 mL of blood — so a BAC of 0.08% means 0.08 grams of alcohol per 100 mL of blood.
Biological sex is one of the most consequential variables in this formula. Women typically have a lower Widmark r-factor (approximately 0.55) compared to men (approximately 0.68), meaning alcohol is distributed through a smaller proportion of body water. Women also tend to have lower levels of alcohol dehydrogenase in the stomach lining, so less alcohol is broken down before it enters the bloodstream. This is why, at identical body weight and drink count, a woman will almost always register a higher BAC than a man — a common mistake people make when estimating their own impairment.
Drink count sounds simple but is frequently underestimated. The calculator uses the concept of a 'standard drink,' which in the US equals 14 grams of pure alcohol — roughly a 12 oz regular beer at 5% ABV, a 5 oz glass of wine at 12% ABV, or a 1.5 oz shot of 80-proof spirits. Craft beers, large wine pours, and cocktails with multiple spirits can easily represent 1.5 to 3 standard drinks in a single serving. Accurately counting your drinks means knowing the ABV and volume of every beverage, not just the number of glasses handed to you.
Time matters significantly because the liver metabolizes alcohol at a fairly constant rate — roughly 0.015% BAC per hour for most adults, though this varies with liver health, food intake, and genetics. The calculator subtracts elapsed time from your estimated peak BAC, which is why drinking the same amount over four hours results in a much lower final BAC than drinking it over one hour. Eating food before or during drinking slows gastric emptying, reducing the peak BAC, but it does not speed up elimination — food 'slows the rise' rather than 'lowering the ceiling.'
Formula
BAC = (drinks·14 / (weight·r)) × 100 − 0.015·hours (Widmark)
Pro tips
- This is a rough estimate only. Never drive after drinking, regardless of the number shown.
Key terms
- Blood Alcohol Content (BAC)
- — A measurement of the concentration of alcohol in the bloodstream, expressed as a percentage of grams of alcohol per 100 mL of blood.
- Widmark Formula
- — A pharmacokinetic equation developed by Erik Widmark used to estimate BAC based on alcohol consumed, body weight, biological sex, and time elapsed.
- Widmark r-Factor
- — A sex-specific constant representing the fraction of body weight through which alcohol is distributed — approximately 0.68 for men and 0.55 for women.
- Standard Drink
- — A unit containing 14 grams of pure alcohol, equivalent to a 12 oz beer at 5% ABV, 5 oz of wine at 12% ABV, or 1.5 oz of 80-proof spirits in the United States.
- Alcohol Elimination Rate
- — The speed at which the liver metabolizes alcohol, typically averaging 0.015% BAC per hour in healthy adults.
- Legal Limit
- — The maximum BAC at which a person is legally permitted to drive; in the United States and many other countries this is 0.08%, though some countries and US commercial driving standards use 0.05% or lower.
