Blood Alcohol Calculator

Swedish physiologist Erik M. P. Widmark published the equation in 1932 (Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung). His work, based on alcohol distribution into total body water, has been the backbone of forensic BAC estimation for nearly a century. The 5.14 unit factor used in this calculator converts ounces of pure ethanol into BAC percent (grams of ethanol per 100 mL of blood) for a given weight in pounds, and the r distribution ratio (0.68 for men, 0.55 for women on average) reflects sex differences in body water content. Later refinements by Forrest (1986) and Watson (1981) added height and age corrections, but Widmark's original formulation is still the standard taught in toxicology and used in calculators like this one.

Most states use a 0.08 percent per se limit for drivers 21 and older, while Utah uses 0.05 percent. Commercial and under-21 rules can be lower, and a driver can be impaired below a numeric threshold. This calculator does not determine legal status, driving fitness, or actual impairment. If you have been drinking, do not drive.

The biggest reason is body composition. Women generally have a lower proportion of total body water than men of the same weight (about 50 to 55 percent versus 60 to 65 percent), so the same amount of ethanol distributes into a smaller fluid volume and reaches a higher blood concentration. The Widmark r ratio reflects this directly: about 0.55 for women versus 0.68 for men. A secondary factor is alcohol dehydrogenase (ADH) activity in the stomach lining, which is lower in women on average, meaning more ethanol survives first-pass metabolism and enters the bloodstream. The result is that a 150 lb woman and a 150 lb man drinking the same two glasses of wine will not end up at the same BAC, and the woman's number will usually be 30 to 40 percent higher.

The 0.015 percent per hour figure is the average ethanol elimination rate measured across hundreds of healthy adults in studies summarized by Jones (Forensic Science International, 2010). Individual rates range from about 0.010 percent per hour in slow metabolizers up to roughly 0.025 percent per hour in heavy drinkers (whose livers up-regulate the microsomal ethanol-oxidizing system), but 0.015 is the published mean and the default in most forensic models. The rate is roughly zero-order under typical drinking conditions, meaning your body clears a fixed amount per hour regardless of how high your BAC starts. Coffee, cold showers, exercise, and water do not speed this up. Only time lowers BAC. The hours-to-sober result is simply current BAC divided by 0.015.

Food slows alcohol absorption rather than reducing total alcohol intake. A solid meal eaten before or during drinking, especially one with protein and fat, keeps the stomach valve (pylorus) closed longer, delaying ethanol passage into the small intestine where most absorption happens. Studies show that eating before drinking can cut peak BAC by 30 to 50 percent compared with drinking on an empty stomach, even though total alcohol consumed is identical. The Widmark formula does not model this and will overestimate peak BAC for someone who drank with a full meal and underestimate it for someone drinking on an empty stomach. The same caveat applies to medications, illness, hydration status, and genetic variation in ADH and ALDH enzymes. Treat the estimate as a ballpark, never as a substitute for a breathalyzer or a decision tool for driving.