Estimate blood alcohol concentration (BAC) using the Widmark formula, based on drinks consumed, body weight, gender, and time elapsed since drinking began.
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This calculator uses the Widmark formula, a standard method for estimating BAC: BAC = (total alcohol consumed in grams ÷ (body weight in grams × distribution ratio)) × 100, minus the alcohol eliminated over time at a typical average rate of about 0.015% per hour. The distribution ratio (0.68 for men, 0.55 for women, on average) reflects that alcohol distributes through body water, and body water proportion differs between sexes on average.
A standard drink is commonly defined as containing about 14 grams of pure alcohol (roughly a 12 oz beer, a 5 oz glass of wine, or a 1.5 oz shot of spirits in the US), adjustable if you're measuring differently.
For example, a 75 kg man who has had 3 standard drinks (3 × 14 = 42 grams of alcohol) over the last 2 hours: raw BAC = (42 ÷ (75,000 × 0.68)) × 100 = (42 ÷ 51,000) × 100 ≈ 0.0824%. Subtracting elimination of 0.015 × 2 = 0.03% over those 2 hours gives an estimated BAC of about 0.052%, in the 'Mild Impairment' range.
This calculator provides a rough mathematical estimate only. Actual BAC is affected by many factors this formula cannot fully account for, including food intake, drinking rate, medications, individual metabolism, and body composition, and it is not a reliable way to determine whether it's safe for you or anyone else to drive or perform other tasks requiring sobriety. Never use this or any BAC estimate as the basis for deciding to drive; when in doubt, don't.
There is no BAC number from this or any calculator that makes it safe to drive after drinking. The only safe approach is to not drink and drive at all: arrange a designated driver, rideshare, taxi, or public transit before you start drinking, not after, regardless of what number this tool shows.
Using any BAC number, including this estimate, to decide whether it's safe to drive, no calculated BAC makes driving after drinking safe; the only safe choice is a designated driver, rideshare, taxi, or public transit, arranged before drinking starts.
Treating this estimate as a reliable way to judge impairment generally, individual factors (food intake, medications, drinking rate, metabolism) can shift real BAC well away from this rough estimate in either direction.
Assuming BAC declines instantly once drinking stops, elimination proceeds at a roughly constant rate per hour, not immediately, so BAC can still be rising for a while after the last drink as absorption catches up.
Using a generic 14g standard drink size for a drink that's actually stronger or larger, cocktails, craft beers, and generous pours often contain meaningfully more alcohol than a standard reference drink.
No. This is a rough estimate for educational purposes only, individual factors can cause your actual BAC to differ meaningfully from this estimate. Never use a BAC calculator, this one or any other, to decide whether it's safe to drive.
There is no BAC number, from this calculator or any other source, that makes driving after drinking safe. The only safe option is not to drive at all: use a rideshare, taxi, public transit, or a designated driver who hasn't been drinking. Plan this before you start drinking, not after, regardless of how low this tool's estimate looks.
In the US, a standard drink is generally defined as about 14 grams of pure alcohol, roughly a 12 oz regular beer, a 5 oz glass of wine, or a 1.5 oz shot of distilled spirits. This can be adjusted in the calculator if your drinks are stronger, weaker, or a different size.
The Widmark formula's distribution ratio reflects average differences in body water percentage between men and women, which affects how alcohol distributes through the body, though individual variation within each gender is significant.
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