Lifestyle & Sleep
BAC Calculator
One drink raises BAC for hours. Estimate your level from what you drank, your weight, and the clock, then see when it returns to zero.
Blood alcohol concentration (BAC) is the percentage of alcohol in blood. The Widmark formula estimates BAC from drinks, body weight, sex, and time. 0.08% is the legal driving limit in most U.S. states — but impairment begins lower.
Legal limit: 0.08% (most US states).
~1 drink raises BAC ≈ 0.02%.
Metabolism ≈ 0.015% per hour.
Calculate Your Blood Alcohol (BAC)
Estimated BAC
What Is Blood Alcohol (BAC)?
Blood alcohol concentration (BAC) is the weight of alcohol per volume of blood, shown as a percentage. In most U.S. states the driving limit is 0.08%; Utah uses 0.05%, and many countries 0.05% or lower.
The Widmark formula estimates BAC from alcohol consumed, body weight, sex, and elapsed time, assuming metabolism near 0.015% per hour.
How It Is Calculated
BAC% = grams alcohol ÷ (weight × r × 10) − 0.015 × hours
r = 0.68 (men) · 0.55 (women)
Example: Example: 75 kg man, 4 drinks over 2 hours → BAC ≈ 0.08%
BAC effects (general population)
| BAC | Typical effects |
|---|---|
| 0.02% | Mild relaxation, slight warmth |
| 0.05% | Reduced coordination, impaired judgment |
| 0.08% | Legal limit, clear motor impairment |
| 0.15% | Significant impairment, slurred speech |
| 0.30%+ | Stupor; medical emergency risk |
Limitations
- Food slows absorption, estimates can overshoot or undershoot.
- Body composition, medications, and liver health change metabolism.
- Never use this to decide whether to drive.
- Standard drink sizes are often exceeded in practice.
Sources & Review
References used for this calculator’s formulas and thresholds:
Blood Alcohol (BAC) FAQ
How long does alcohol stay in your system?
BAC falls about 0.015% per hour, roughly one standard drink per hour. From 0.08%, expect about 5–6 hours to zero.
How many drinks is 0.08 BAC?
For a 75 kg man, roughly 4 standard drinks in 2 hours; for a 60 kg woman, about 2–3. Size, food, and pace change this.
Does coffee or water sober you up?
No, only time lowers BAC. Coffee makes you a wide-awake impaired driver.
Is the Widmark formula accurate?
It estimates within roughly ±0.02% for average adults, useful educationally, never for safety decisions.
A note before you begin: this tool offers educational estimates only. It cannot replace advice from a qualified professional.