Blood Alcohol Content (BAC) Calculator
The Widmark formula behind every BAC chart — and the honest reasons it can never tell you it is safe to drive.
Estimate your BAC
One standard drink = 12 oz beer (5%) · 5 oz wine (12%) · 1.5 oz spirits (40%)
The Widmark formula
Every BAC chart descends from Erik Widmark's 1932 equation: alcohol consumed (grams) divided by body weight times a distribution constant (≈0.68 for men, 0.55 for women — alcohol distributes into body water, and body composition differs), minus elimination of roughly 0.015% per hour. A standard US drink contains about 14 grams of alcohol regardless of whether it is beer, wine, or whiskey.
Why your real BAC can be higher than this estimate
The formula assumes textbook conditions. Reality intervenes: drinks are over-poured (a generous wine pour or a craft IPA can be 1.5–2 "standard" drinks), empty stomachs speed absorption, medications interact, fatigue amplifies impairment, and individual metabolism varies. Police breathalyzers do not care about your calculator. Treat every estimate as a floor, not a ceiling.
The numbers that matter — and the one rule
Impairment begins around 0.02% — divided attention and tracking degrade long before anyone feels "drunk." At 0.05%, crash risk roughly doubles; at 0.08% (the legal limit in most US states; 0.05% in Utah) it is several times baseline. Commercial drivers are held to 0.04%, under-21 drivers to near zero. Elimination cannot be rushed: coffee, cold showers, and food make you an alert person with the same BAC. The only honest use of this calculator is appreciating how long alcohol persists — three drinks can take five-plus hours to fully clear. If you have been drinking at all, the driving decision is already made: ride share, taxi, or a sober friend. In Las Vegas, the ride costs less than the valet at most casinos — and infinitely less than a DUI.
Frequently asked questions
How long until I am at zero?
Elimination averages ~0.015% per hour and nothing accelerates it. The calculator shows the estimate — note that one evening of heavy drinking can leave measurable BAC the next morning.
Is 0.08 the limit everywhere?
It is the standard in most US states; Utah uses 0.05, commercial drivers face 0.04, and under-21 drivers face zero-tolerance limits. You can also be charged below 0.08 if demonstrably impaired.
Why do women reach higher BAC on the same drinks?
On average lower body water percentage (the Widmark r of 0.55 vs 0.68), so the same alcohol concentrates more. Body size compounds the effect.
Does eating before drinking lower BAC?
Food slows absorption, flattening the peak — but the same alcohol still enters your blood and takes just as long to eliminate. It buys gentleness, not sobriety.