Blood Alcohol (BAC) Calculator
Estimate your blood alcohol level.
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- No sign-up
- Private — runs in your browser
- Instant results
What blood alcohol content means
Blood alcohol content (BAC) is the percentage of alcohol in your bloodstream. A BAC of 0.08% — the legal driving limit in most US states — means 0.08 grams of alcohol per 100 millilitres of blood. This calculator estimates BAC using the Widmark formula, the standard method that factors in how much you drank, your body weight, your sex, and how long ago you started.
How the estimate is calculated
The formula is BAC = (alcohol in grams ÷ (body weight in grams × r)) × 100 − (0.015 × hours).
The r value reflects how alcohol distributes through body water — about 0.68 for men
and 0.55 for women, since body composition differs. Your liver then clears alcohol at roughly
0.015% per hour, which is why BAC falls steadily once you stop drinking and can't
be sped up by coffee, water, or a cold shower.
What counts as one standard drink
A US standard drink contains about 14 grams of pure alcohol, which is roughly:
- 12 oz of regular beer (about 5% ABV)
- 5 oz of wine (about 12% ABV)
- 1.5 oz of distilled spirits (about 40% ABV)
Strong craft beers, large pours, and cocktails often count as more than one standard drink.
Important: this is an estimate only
Real BAC depends on many things this formula can't capture — food in your stomach, medications, hydration, drinking pace, metabolism, and individual tolerance. Never use this tool to decide whether you're safe to drive. If you've been drinking, don't drive. The only way to reach 0.00% is time.
FAQ
Why does the same drink affect people differently?
Body weight and composition change how alcohol is diluted, and sex affects the body-water ratio. A smaller person reaches a higher BAC from the same number of drinks than a larger one.
Can I sober up faster?
No. Your liver clears alcohol at a roughly fixed rate. Coffee, food, and water may make you feel more alert but do not lower your BAC — only time does.
Is the legal limit always 0.08%?
For most US drivers it's 0.08%, but it's lower for commercial drivers and drivers under 21, and some places use 0.05%. Penalties can apply below the limit if you're visibly impaired.