Fitness & Health Calculators

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BAC Calculator

The Blood Alcohol Concentration (BAC) Calculator estimates the percentage of alcohol in your bloodstream. Calculations are based on the Widmark formula, adjusting for biological sex, body weight, quantity of alcohol, and time elapsed since consumption began.

Important Legal Disclaimer

This calculator provides mathematical estimates based on average metabolism rates. It is for educational purposes only and must not be used to determine if it is safe or legal to drive. Biological factors like food intake, liver health, genetics, and medication can dramatically alter actual blood alcohol levels. If you have consumed alcohol, do not drive.

Sex impacts body water distribution (r-value: male ≈ 0.68, female ≈ 0.55), altering peak alcohol concentration.
kg
Please enter a valid body weight (30–250 kg).
drinks
Please enter standard drink quantity (1–30).
Please select a drink type.
hrs
Please enter valid elapsed hours (0–24).
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How is BAC Calculated? (The Widmark Equation)

Blood Alcohol Concentration (BAC) measures the percentage of alcohol present in a person's bloodstream. The standard mathematical model for estimating BAC is the Widmark Formula, developed in 1932 by Swedish researcher Erik M. P. Widmark.

The formula is structured as follows:

BAC (%) = [ (A / (W × 1000 × r)) × 100 ] - (β × H)

Where:

  • A: Mass of pure alcohol consumed in grams. (One standard drink in the United States/UK contains approximately 14 grams of pure ethanol).
  • W: Body weight in kilograms. (Multiplied by 1,000 to convert to grams).
  • r: Gender-specific body water distribution constant. Men have a higher percentage of water on average (r = 0.68) than women (r = 0.55).
  • β: Alcohol elimination rate. The human body metabolizes alcohol at a linear rate. The standard average metabolic clearance rate used is 0.015% per hour.
  • H: Elapsed time in hours since drinking began.

What constitutes a Standard Drink?

In many physiological models, a standard drink contains exactly 14 grams of pure alcohol. This matches typical serving sizes of common beverages:

  • Beer (12 fl oz / 355 ml): Typically at 5% alcohol by volume (ABV).
  • Wine (5 fl oz / 148 ml): Typically at 12% alcohol by volume (ABV).
  • Spirits / Distilled Shot (1.5 fl oz / 44 ml): Typically at 40% alcohol by volume (ABV, or 80 proof).

Different craft beers, fortified wines, and mixed cocktails can have much higher alcohol percentages. If you consume high-gravity or oversized drinks, adjust the count accordingly.

BAC Reference Table (Peak BAC by Weight and Drinks)

The table below indicates the estimated peak blood alcohol concentration (BAC %) immediately after drinking (0 hours elapsed) for a male (r = 0.68) at various body weights.

Body Weight 1 Standard Drink 2 Standard Drinks 3 Standard Drinks 4 Standard Drinks 5 Standard Drinks
50 kg (110 lbs) 0.041% 0.082% 0.124% 0.165% 0.206%
60 kg (132 lbs) 0.034% 0.069% 0.103% 0.137% 0.172%
70 kg (154 lbs) 0.029% 0.059% 0.088% 0.118% 0.147%
80 kg (176 lbs) 0.026% 0.051% 0.077% 0.103% 0.129%
90 kg (198 lbs) 0.023% 0.046% 0.069% 0.092% 0.114%
100 kg (220 lbs) 0.021% 0.041% 0.062% 0.082% 0.103%

Note: Legal driving limits across most regions globally range from 0.05% to 0.08%. Females will experience higher peak BACs at corresponding weights due to lower body water distribution.

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