Blood Alcohol Content (BAC) Calculator

This is an estimate, and a rough one. Real BAC depends on food, hydration, medication, health, drinking speed and individual metabolism — variables no formula can capture. It can easily read lower than your true level. The only safe amount of alcohol before driving is none. If you have been drinking, do not drive; use a taxi, rideshare, public transport or a sober driver.

BAC is the alcohol in your blood as a percentage. The Widmark estimate is: BAC = (alcohol in grams × 100) / (body weight in grams × r) − 0.015 × hours where r is a distribution factor — about 0.68 for men and 0.55 for women, reflecting differences in body water. One US standard drink is 14 g of pure alcohol, and your body clears roughly 0.015% per hour, which is the subtraction at the end. That elimination rate is fixed — only time lowers BAC. Coffee, water and cold showers do nothing to it.

In the United States it is illegal to drive at 0.08% or above (0.05% in many other countries, and lower or zero for commercial and young drivers). But impairment of reaction time and judgment begins well below any legal limit — often from the first drink. A low estimate here is not a safe estimate. Also note BAC keeps rising for 30–90 minutes after your last drink as alcohol is still being absorbed, so a reading taken now can climb.