This calculator uses the Widmark formula to estimate blood alcohol content (BAC) from the number of standard drinks, body weight, sex and the hours since your first drink. It is a rough educational estimate: real BAC varies enormously with food, drink strength, medication, health and metabolism. It cannot, and must not, be used to judge whether you are safe or legal to drive.
Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: the Widmark formula, recomputed in code. Not medical or legal advice.
The Widmark formula
Each US standard drink holds about 0.6 fluid ounces of pure alcohol, so A is the drink count times 0.6. The constant 5.14 converts ounces and pounds into a BAC percentage, r is the body-water distribution ratio, and 0.015 per hour is the average rate the body clears alcohol. Because only time lowers BAC, the longer since your first drink, the more is subtracted.
Worked example
A 180 lb man, 4 standard drinks, 2 hours:
The estimate is about 0.064% — below the US 0.08% driving limit, but still impaired. A 140 lb woman with 3 drinks in 1 hour estimates near 0.085%, over the limit. These are averages; an individual could be well above or below, which is exactly why an estimate can never green-light driving.
Frequently Asked Questions
BAC% = (drinks×0.6 × 5.14) / (weight_lb × r) − 0.015 × hours. r ≈ 0.73 (M), 0.66 (F). An estimate only.
~0.6 fl oz (14 g) pure alcohol: a 12 oz 5% beer, 5 oz 12% wine, or 1.5 oz shot of 40% spirits.
US is 0.08% (0.04% commercial, zero under 21). Limits vary by country. Alcohol impairs even below the limit.
Rough. It ignores food, drink strength, meds, health and metabolism. Only a breath/blood test is real. Never rely on it to drive.
About 0.015%/hour, and only time helps — coffee and water don't. From 0.08% that's 5+ hours to zero on average.