Blood Alcohol Content (BAC) Calculator
A rough Widmark-formula estimate of blood alcohol content — never a signal to drive.
Estimated BAC Level
SAFE LEVEL
DISCLAIMER: This is an estimation for educational purposes only. Do not rely on this to determine your ability to drive. Never drink and drive.
This tool gives a rough estimate of blood alcohol content (BAC) from the number of standard drinks, your body weight, your sex, and the time since you started drinking. It's here to illustrate how quickly alcohol adds up and how slowly the body clears it — not to tell you whether you're okay to drive. No calculator can do that safely, and the only reliable amount of alcohol before driving is none. Everything is worked out in your browser.
The Widmark formula
The estimate uses the Widmark equation, treating each standard drink as 14 grams of alcohol and subtracting the alcohol the body metabolises over time at about 0.015% per hour:
BAC = (alcohol grams ÷ (body weight in g × r)) × 100 − (0.015 × hours)
Here r is a body-water constant — about 0.68 for men and 0.55 for women. Because it relies on averages, the result can differ substantially from your true BAC, which is affected by food, medications, hydration, health, drinking speed, and how a "drink" is actually poured. A generous home pour can hold far more than one standard drink, throwing the estimate off entirely.
Impairment starts long before any legal limit
Alcohol begins impairing judgement, reaction time, and coordination from the very first drink — well below 0.08%, and below any threshold this tool might label. A number under a legal limit is not a green light: people are arrested, cause crashes, and are harmed at low BAC levels every day, and limits are lower or zero for commercial and young drivers. Never use this estimate to decide whether to drive, operate machinery, or do anything requiring full alertness. If you've been drinking, arrange a taxi, rideshare, public transport, or a sober driver. When in doubt, don't drive.
Frequently Asked Questions
Can this tell me if I'm safe to drive?
No — and you should never use it that way. It is a rough average-based estimate that can be well off from your real BAC, and impairment begins with the first drink regardless of the number shown. If you have consumed any alcohol, the safe choice is not to drive.
Why might my real BAC differ from the estimate?
Because the formula uses population averages. Your actual level depends on food in your stomach, medications, hydration, body composition, health, how fast you drank, and how much alcohol was really in each drink — a heavy pour can far exceed one standard drink.
What is a standard drink?
This tool treats one standard drink as about 14 grams of pure alcohol — roughly a 12 oz regular beer, 5 oz of wine, or 1.5 oz of distilled spirits. Cocktails and large or strong pours often contain several standard drinks.
Is my data saved?
No. The calculation runs entirely in your browser and nothing you enter is uploaded or stored.