BAC Calculator (Widmark Formula)

This BAC calculator estimates blood alcohol content using the classic Widmark formula, the same equation forensic toxicology and public-health education have used for decades: BAC% = (A / (W × r)) × 100 − (β × t). A is the total grams of alcohol you consumed, W is your body weight in grams, r is the sex-specific Widmark distribution ratio (about 0.68 for men and 0.55 for women, reflecting average differences in body water content), β is the average elimination rate of about 0.015% of BAC per hour, and t is the hours elapsed since you started drinking.

Rather than assume a vague "one drink equals one unit", the calculator asks for the real volume and ABV% of each drink so it can compute grams of alcohol directly: grams = volume in milliliters × (ABV ÷ 100) × 0.789, where 0.789 g/ml is the density of pure ethanol. Quick presets fill in typical serving sizes for beer, wine and spirits, or you can enter any custom volume and strength. Add as many drinks as you like — the calculator sums the alcohol from all of them before applying the formula.

Every number in the formula is shown substituted with your actual inputs, so nothing about the estimate is hidden: the grams of alcohol, your weight converted to grams, the distribution ratio used for your selected sex, the elimination rate, and the hours elapsed all appear in the final calculation line. If the elimination term would push the result below zero, the estimate is clamped at 0% rather than shown as negative.

Please read this carefully: this tool produces an educational estimate only, not a measurement of your actual blood alcohol content. Real BAC varies significantly between individuals and even between occasions for the same person, depending on food intake, medications, hydration, metabolism, liver function, and many other factors this formula cannot see. It must never be used to decide whether it is safe to drive, operate machinery, or do anything else that requires being unimpaired. If you have been drinking, call a cab, use a rideshare, or ask a designated driver — do not rely on this or any calculator to judge your own sobriety.