Blood Alcohol Concentration Calculator
Blood Alcohol Concentration (BAC) measures the amount of alcohol in your bloodstream. This calculator uses the Widmark formula to estimate your BAC based on drinks consumed, body weight, gender, and time elapsed. Results are estimates only.
—
Blood Alcohol Concentration
References
- Watson, P. E., Watson, I. D., & Batt, R. D. (1981). Prediction of blood alcohol concentrations in human subjects: updating Widmark Equation. Journal of Studies on Alcohol, 42(7), 547-556. PubMed
- Posey, D., & Mozayani, A. (2007). The estimation of blood alcohol concentration. Forensic Science, Medicine, and Pathology, 3(1), 33-39. PubMed
Legal Limits by Country
| Country/Region | Limit |
|---|---|
| USA, UK, Canada | 0.08% |
| Australia, New Zealand | 0.05% |
| Most of Europe (Germany, France, Italy, Spain, etc.) | 0.05% |
| Japan, South Korea | 0.03% |
| Nordic countries (Norway, Sweden, Finland) | 0.02% |
| Some jurisdictions (zero tolerance) | 0.00% |
This table is for reference only. Laws change and vary within countries. Always verify current local laws before driving.
Frequently Asked Questions
The Widmark formula, developed in the 1930s and refined by Watson et al. (1981), predicts BAC within 10-20% accuracy for most individuals. It uses body weight and gender-specific body water ratios (0.68 for males, 0.55 for females) to estimate alcohol distribution. However, individual variations in metabolism, body composition, and genetics mean actual BAC can differ significantly from calculated estimates.
Multiple variables influence BAC beyond weight and gender. Food in the stomach can slow absorption by 25-50%, with high-fat meals most effective. Carbonated beverages accelerate absorption. Genetic variations in alcohol dehydrogenase enzymes cause 10-fold differences in metabolism rates among individuals. Asian populations often have altered enzyme activity. Medications, hydration, and hormonal cycles also affect absorption unpredictably.
Women typically achieve higher BAC than men of equal weight consuming identical amounts. Research by Frezza et al. (1990) identified two primary factors: lower body water percentage (55% vs 68%) concentrates alcohol more, and reduced gastric alcohol dehydrogenase activity in women means more alcohol enters the bloodstream unchanged. These physiological differences result in approximately 30% higher BAC in women.
Legal driving limits range from 0.00% (zero tolerance) in countries like Saudi Arabia and UAE, to 0.08% in the US, UK, and Canada. Most European nations use 0.05%, while Sweden and Norway enforce 0.02%. Japan and South Korea set limits at 0.03%. These variations reflect different cultural attitudes toward alcohol and traffic safety. Notably, impairment begins well before legal limits.
The liver eliminates alcohol at approximately 0.015-0.020% BAC per hour, equivalent to roughly one standard drink. This rate is consistent regardless of BAC level, as alcohol dehydrogenase enzymes become saturated (zero-order kinetics). Contrary to popular belief, coffee, food, or exercise cannot accelerate this rate. A person at 0.08% BAC requires approximately 5-6 hours to reach zero.
Impairment begins at the first drink. NHTSA research demonstrates measurable reaction time and judgment impairment at 0.02% BAC. At 0.05%, coordination and ability to track moving objects decline. The legal limit of 0.08% does not represent safe driving; crash risk increases approximately 4-fold at this level. Studies show even 0.01% BAC slightly increases crash probability.