BAC Calculator
Calculate Blood Alcohol Concentration (BAC) using the Watson formula. More accurate than traditional Widmark equation with precise alcohol-to-grams conversion.
Personal Information
Alcohol Consumed
Drink 1
Metric Widmark Formula: BAC(%) = A_g ÷ (r × W_kg × 10) - (β × t)
A_g = alcohol grams, r = distribution ratio (male: 0.68, female: 0.55), β = 0.017/hour elimination
Enter your information and drinks, then click Calculate to see BAC.
What is BAC?
Blood Alcohol Concentration (BAC) measures the amount of alcohol in your bloodstream as a percentage. This calculator uses the Watson formula for more accurate Total Body Water calculation compared to traditional Widmark equation.
Watson vs Widmark Formula
- Watson: Uses age, height, weight, and gender for precise TBW
- Widmark: Uses simple gender constants (less accurate)
- Elimination rate: 0.017/hour (more accurate than 0.015)
- Alcohol conversion: Volume × ABV × 0.789 density
Metric Widmark Formula
- Formula: BAC(%) = A_g ÷ (r × W_kg × 10) - β × t
- Distribution ratios: Male 0.68, Female 0.55 (metric constants)
- Elimination rate: 0.017% per hour (updated standard)
- Alcohol conversion: Volume(ml) × ABV% × 0.789 density
Standard Drink Equivalents
1 Standard Drink = 14g pure alcohol:
• 12 oz beer (5% ABV)
• 5 oz wine (12% ABV)
• 1.5 oz liquor (40% ABV)
Elimination Rate:
The liver eliminates alcohol at approximately 0.017% BAC per hour (updated from older 0.015 rate), regardless of body size or drinking experience.
Safety Note: This calculator is for educational purposes only. Never rely on BAC estimates to determine if you're safe to drive.