The Drinkmeter estimation engine is built upon the Widmark Formula, the most widely accepted mathematical model for calculating Blood Alcohol Concentration (BAC). Our tool computes the mass of pure alcohol consumed and projects its concentration in the blood based on body weight, gender-specific distribution constants, and elapsed time.
The Formula
BAC % = [ Alcohol (g) / (Weight (g) × r) ] × 100 - (t × β)
Alcohol (g): Mass of pure ethanol consumed.
Weight (g): Body weight in grams.
r: The Widmark factor (volume of distribution).
t: Time elapsed in hours.
β: The metabolic elimination rate.
Key Constants & Variables
- Alcohol Mass Calculation: We convert liquid volume to mass using the density of ethanol (0.789 g/ml).
Formula: Volume (ml) × (ABV% / 100) × 0.789 - Widmark Factor (r): This constant represents the proportion of body mass that holds water. We utilize the standard average values:
- Males: 0.68
- Females: 0.55
- Elimination Rate (β): The liver metabolizes alcohol at a relatively constant rate. Our calculator uses the mean elimination rate of 0.015% per hour.
Standard Drink Definition
For comparative purposes, Drinkmeter adheres to the National Institute on Alcohol Abuse and Alcoholism (NIAAA) guidelines. We define one "Standard Drink" as containing roughly 14 grams of pure alcohol.
Algorithmic Limitations
While the Widmark formula provides a scientific baseline, it is a mathematical approximation that cannot account for individual biological variances. Real-world BAC is influenced by factors our calculator cannot measure:
- Food Consumption: Eating before or during drinking significantly slows absorption.
- Medication interactions: Certain drugs can intensify alcohol effects.
- Metabolic Variance: Individual elimination rates can range from 0.010% to 0.025% per hour.
- Hydration & Fatigue: Physical state affects how alcohol is processed.