Estimate BAC from drinks consumed, body weight, gender, and time elapsed using the Widmark formula.
This calculator runs the Widmark formula: it converts every drink you log into grams of pure alcohol, divides that by your body weight scaled by a sex-specific distribution ratio (about 0.68 for men, 0.55 for women in the classic formula), then subtracts roughly 0.015% for each hour since you started drinking to account for elimination. The number it returns is a population-average estimate, not a measurement. What trips people up most is treating a 'drink' as one unit regardless of size or strength - a double pour or a high-ABV craft beer counts as more than one standard drink, and entering it as one will understate the result.
A concrete input and expected output from the current implementation.
Input
3 standard drinks (14g alcohol each), 180 lb, male, 2 hours since the first drink
Expected output
Estimated BAC: approximately 0.046% (about 0.05% rounded to two decimals)
42g of alcohol divided by (180 lb converted to 81,647g x 0.68) gives 0.0757%, and subtracting 0.015% x 2 hours of elimination leaves about 0.046%.
Each drink is converted to grams of pure alcohol from its volume and ABV - a standard 12 oz beer at 5% ABV works out to roughly 14 grams. The calculator sums these grams across every drink entered before the distribution step, so how you log pour size and proof matters as much as how many drinks you say you had.
Total alcohol grams are divided by body weight in grams multiplied by a distribution ratio r (about 0.68 for men, 0.55 for women), which models how alcohol spreads through body water. The tool then subtracts about 0.015 percent for every hour since the first drink, representing the average rate the liver metabolizes alcohol.
No. This is a rough statistical estimate built on population averages, not a reading of your actual blood alcohol level, and it can be off by a meaningful margin either direction. Wait it out, use a certified breathalyzer, or arrange another ride instead of relying on this figure for that decision.
The Widmark formula applies a different distribution ratio (r) for men and women because average body water percentage differs between the two, which changes how the same amount of alcohol dilutes. The tool offers the two standard Widmark categories, so it does not model individual variation outside that binary assumption.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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