Blood Alcohol Content Calculator

In the United States, the federal guideline for blood alcohol concentration (BAC) for driving a motor vehicle is 0.08% (80 mg of alcohol per 100 ml of blood) for adults aged 21 and over. For commercial vehicle drivers the limit is 0.04%. For drivers under 21, zero-tolerance laws in most states set limits at 0.00% to 0.02%. State laws vary; always check your state's specific rules.

The Widmark formula provides a population-average estimate of BAC with accuracy typically within 0.01 to 0.02 percentage points for most adults. Individual variation in alcohol dehydrogenase enzyme activity, food consumption, hydration, body composition, and other factors can cause actual BAC to vary significantly from the estimate. This calculator is educational, not a substitute for a certified breathalyzer test.

In the United States, one standard drink contains approximately 14 grams (0.6 fluid ounces) of pure alcohol. This equates to: 12 fl oz of regular beer (about 5% ABV), 5 fl oz of wine (about 12% ABV), or 1.5 fl oz of distilled spirits (about 40% ABV). Many craft beers and cocktails contain significantly more than one standard drink per serving.

The body metabolises alcohol at a roughly constant rate of approximately 0.015% BAC per hour for most adults, regardless of body weight, food intake, coffee, cold showers, or exercise. The Widmark formula uses this elimination rate. Starting at 0.10% BAC, it would take approximately 6 to 7 hours to reach 0.00%. Only time reduces BAC.

Tolerance (regular drinkers feel less impaired at the same BAC), food in the stomach (slows absorption), carbonation (speeds absorption), sex and hormonal cycle, fatigue, and medications all affect subjective intoxication. However, driving impairment from alcohol is measurable at BAC levels below 0.08%, including from 0.02% onwards for reaction time and cognitive tasks.