Blood Alcohol Content (BAC) is measured as grams of alcohol per 100 mL of blood. A BAC of 0.08% is the legal limit for driving in most US states.
Widmark Formula
BAC = (Alcohol in grams / (Body weight in grams × r)) − (0.015 × hours), where r = 0.68 for men, 0.55 for women.
Effects by BAC Level
- 0.02%: Mild relaxation, slight mood elevation
- 0.05%: Reduced inhibitions, impaired judgment
- 0.08%: Legal limit — poor coordination, slower reaction time
- 0.15%: Major impairment of balance and movement
- 0.30%+: Risk of loss of consciousness or death
Factors the Widmark Formula Doesn't Fully Capture
The formula assumes even alcohol distribution and steady metabolism, but actual BAC is affected by food in the stomach (slows absorption), medications, liver health, and even genetics — meaning two people of identical weight and gender can reach different actual BAC from the same drinks. Estimators are a guide, not a substitute for not driving after drinking.
Standard Drink Sizes
A "standard drink" in the U.S. is 14 grams of pure alcohol: 12 oz of regular beer (~5% ABV), 5 oz of wine (~12% ABV), or 1.5 oz of 80-proof spirits. Craft beers and mixed drinks often contain significantly more alcohol than a standard drink, which is a common source of underestimating BAC.