The Widmark Formula
BAC = (A × 5.14) / (W × r) − 0.015 × H
Where:
A = total alcohol consumed in oz (standard drinks × 0.6)
W = body weight in pounds
r = Widmark factor (0.73 for men, 0.66 for women)
H = hours since first drink
0.015 = alcohol elimination rate per hour
Widmark Factor Explained
The Widmark factor (r) accounts for the difference in body water distribution between men and women. Men have more muscle mass and less body fat, which means alcohol distributes into a larger volume of body water — resulting in lower BAC for the same amount consumed.
- Men: r = 0.68–0.73 (use 0.73 for conservative estimate)
- Women: r = 0.55–0.66 (use 0.66 for conservative estimate)
- Athletes: Higher r value (more muscle mass)
- Higher body fat: Lower r value
Worked Example
Scenario: 160 lb man, 3 standard drinks, over 2 hours
- A = 3 drinks × 0.6 oz = 1.8 oz alcohol
- W = 160 lbs
- r = 0.73 (male)
- H = 2 hours
BAC = (1.8 × 5.14) / (160 × 0.73) − 0.015 × 2
BAC = 9.252 / 116.8 − 0.03
BAC = 0.0792 − 0.03 = 0.049%
Below legal limit (0.08%) but still impaired — judgment and reaction time are affected at 0.05%+
Frequently Asked Questions
What is the Widmark formula?
The Widmark formula is a mathematical model developed by Swedish scientist Erik Widmark in 1932 for estimating blood alcohol concentration (BAC) based on body weight, gender, drinks consumed, and time elapsed.
How accurate is the Widmark formula?
The formula is accurate within ±0.01%–0.02% BAC for most people under controlled conditions. Actual BAC varies with food intake, metabolism, medications, and individual physiology. Use results as estimates only.
What is the alcohol elimination rate of 0.015% per hour?
The liver metabolizes alcohol at a relatively constant rate of approximately 0.015% BAC per hour (about one standard drink per hour). This rate cannot be increased by coffee, water, food, or exercise.
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