Blood Alcohol (BAC) Calculator
Estimate your blood alcohol content (BAC) using the Widmark formula. Enter your drinks, body weight, and time elapsed to get an instant estimate in your browser.
This is an estimate only. Never drink and drive. This calculator does not constitute medical or legal advice.
How BAC is calculated
This calculator uses the Widmark formula, the most widely cited method for estimating blood alcohol content. The formula accounts for the total grams of alcohol consumed, your body weight, biological sex (which affects the Widmark distribution ratio — 0.68 for males, 0.55 for females), and the hours elapsed since drinking began. Metabolism burns off approximately 0.015% BAC per hour. All calculations happen entirely in your browser; nothing is uploaded or stored.
The formula: BAC = (grams of alcohol ÷ (body weight in grams × r)) × 100 − 0.015 × hours. Grams of alcohol = drinks × volume (ml) × (ABV ÷ 100) × 0.789.
FAQ
What does BAC mean? Blood Alcohol Content is the percentage of alcohol in your bloodstream. A BAC of 0.08% is the legal driving limit in many countries.
How accurate is this estimate? The Widmark formula gives a reasonable approximation but individual results vary based on food intake, metabolism, hydration, and other factors. Always treat this as an estimate, not a precise measurement.
Is my data stored? No. Everything runs client-side in JavaScript. Nothing is uploaded or logged.
Why does sex affect BAC? Biological sex influences the Widmark r-factor, which represents the fraction of body weight that is water. Males typically have a higher water fraction (0.68) than females (0.55), so the same amount of alcohol is more diluted in a male body.