HEALTH · BAC
BAC Calculator
Estimate blood alcohol content using the Widmark formula. For harm-reduction awareness only — never use to decide whether to drive.
Estimate only — individual BAC varies with food intake, medications, metabolic rate, and health conditions.
About This Calculator
The Widmark formula estimates blood alcohol concentration from body weight, biological sex, the number of standard drinks consumed, and time elapsed. It is used in forensic toxicology and is the basis of the NHTSA standard. This tool is for awareness only — individual BAC varies significantly, and no estimate should ever be used to decide whether it is safe to drive.
How It Works
Enter your number of standard US drinks (1 drink = 14 g pure alcohol), body weight, biological sex, and hours since the first drink. The calculator applies a sex-specific distribution constant and subtracts the typical elimination rate of 0.015 g/dL per hour.
The Formula
BAC = A / (r × W × 10) − β × t
- A
- pure alcohol in grams (drinks × 14 g per standard US drink)
- r
- Widmark distribution constant: 0.68 male, 0.55 female
- W
- body weight in kg
- β
- elimination rate: 0.015 g/dL per hour
- t
- hours since first drink
Frequently Asked Questions
- Can I use this to know if I'm safe to drive?
- No. This is a statistical estimate — individual BAC varies with food intake, medications, metabolic rate, fatigue, and health conditions. The formula does not account for impairment, which can occur at any BAC. If you have had any alcohol, the safest choice is not to drive.
- What is a standard US drink?
- 14 grams of pure alcohol, which is approximately 12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% spirits (80-proof liquor).
- Why are different constants used for male and female?
- The Widmark r constant reflects how alcohol distributes in body water. Women typically have proportionally less body water than men of the same weight, meaning the same amount of alcohol concentrates more — reflected in the lower r value (0.55 vs 0.68).