How this calculator works
The Widmark approximation distributes ethanol using ratios of 0.68 for males and 0.55 for females and subtracts an assumed 0.015 g/dL per hour since the first drink. This is a rough healthy-adult estimate, with large variation from absorption, food, physiology and elimination. A US standard drink contains 14 g ethanol; the Canadian standard drink is about 13.45 g. A zero estimate does not establish sobriety. Never use this result to decide whether to drive. The result is an estimate for information only and is not medical advice.
Formula
BAC (g/dL) = max(0, drinks x 14 / (r x weight in kg x 10) - 0.015 x hours). The factor 10 converts the gram-per-kilogram ratio to g/dL. BAC (mg/dL) = BAC (g/dL) x 1000.
Worked example
For 3 US standard drinks, an 80 kg male and 2 hours since the first drink, the estimate is 0.047 g/dL or 47 mg/dL.
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Frequently asked questions
Can I use it to decide whether to drive?
Never. The estimate cannot establish fitness to drive, even if it displays zero.
Are Canadian drinks counted the same way?
This calculation uses 14 g ethanol per drink. Canadian standard drinks contain about 13.45 g, so convert the amount of ethanol rather than assuming the counts match.
Does food or body composition change the estimate?
They are not modelled. The fixed distribution ratios and elimination rate ignore absorption, food and individual physiology, so the result is only a rough average.