BAC Calculator
Estimate your blood alcohol content based on weight, sex, drinks, and time.
This calculator provides estimates for educational purposes only. Never drink and drive. If you've been drinking, always use a designated driver or ride-share service.
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Frequently Asked Questions
How does the BAC calculator work?
This calculator uses the Widmark formula, the most widely accepted scientific method for estimating blood alcohol content. It takes into account your body weight, biological sex (which affects water content and alcohol distribution), the number and type of drinks consumed, and time elapsed since drinking. The formula calculates the peak BAC and then subtracts the body's natural alcohol elimination rate of approximately 0.015% per hour.
What is the legal BAC limit for driving?
In the United States, the legal BAC limit for drivers 21 and over is 0.08% in all 50 states. However, impairment begins well below this level. At 0.02% you may experience altered mood and relaxation, and at 0.05% you may have reduced coordination and impaired judgment. Many countries set their limits at 0.05% or lower. Commercial drivers in the US have a limit of 0.04%, and drivers under 21 face zero-tolerance laws in most states.
How long does it take for BAC to reach zero?
Your body eliminates alcohol at a relatively constant rate of about 0.015% BAC per hour. This means if your BAC is 0.08%, it would take roughly 5.3 hours to reach zero. If your BAC is 0.15%, it could take 10 hours. There is no way to speed up this process. Coffee, cold showers, and exercise do not reduce BAC faster. Only time allows your liver to metabolize the alcohol.
Why does sex affect BAC calculations?
Biological sex significantly affects BAC because of differences in body composition. Females typically have a higher percentage of body fat and lower percentage of body water than males of the same weight. Since alcohol is water-soluble, it becomes more concentrated in a body with less water. The Widmark formula accounts for this with different distribution ratios: 0.68 for males and 0.55 for females.
Is this BAC calculator accurate enough to determine if I can drive?
No. This calculator provides an estimate for educational purposes only and should never be used to decide whether you are safe to drive. Actual BAC depends on many individual factors not captured here, including metabolism, food intake, medications, liver health, hydration, and tolerance. The safest approach is to not drive at all after drinking. Use a designated driver, ride-share service, or wait until you are certain all alcohol has been eliminated.