How to calculate bac
BAC = (drinks × 14 g) ÷ (weight g × r) × 100 − 0.015 × hours
Worked example. Estimated BAC: 0.046%.
Example inputs — Standard drinks: 3; Body weight: 180 lb; Sex: Male; Hours since first drink: 2. Starting values are illustrative.
Below the 0.08% US limit — but any alcohol impairs driving
From George Guju, founder of Calculyn · Educational calculator guidance, not professional advice.
How it works
The Widmark formula estimates BAC from alcohol consumed, body weight and a sex-based distribution factor, minus about 0.015% per hour of metabolism. It's a rough estimate — food, medications and individual metabolism all change the real number.
Assumptions & limitations
- Results are rounded for display.
Formula and assumptions reviewed October 2026 by the Calculyn team. How we build our calculators
Frequently asked questions
What's a standard drink?
12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% spirits — each contains about 14 grams of alcohol.
Can I drive under 0.08%?
Impairment begins well below 0.08%, and some places have lower limits. The only safe BAC for driving is zero.