How the Widmark Formula Works
The Widmark formula is the standard method used to estimate blood alcohol concentration from the amount of alcohol consumed.
The formula is:
BAC (‰) = A / (m × r)
Where: A = mass of pure ethanol consumed (grams), m = body mass (kg), r = Widmark factor (0.68 for men, 0.55 for women)
Step-by-step breakdown
- Calculate ethanol volume: Drink volume (ml) × ABV (%) / 100
- Convert to grams: Ethanol volume (ml) × 0.789 g/ml (density of ethanol)
- Apply Widmark formula: Total ethanol (g) / (body weight in kg × Widmark factor)
- Estimate elimination time: BAC (‰) / 0.12 ‰ per hour (average metabolic rate)
Why men and women differ
Women generally have a higher body fat percentage and lower water content than men of the same weight. Since alcohol distributes through body water, women reach higher BAC levels from the same amount of alcohol — hence the lower Widmark factor (0.55 vs 0.68).
Standard Drink Sizes
A "standard drink" contains approximately 14 grams (0.6 oz) of pure alcohol. Here's what that looks like for different beverages:
| Drink | Typical ABV | Standard drink volume | Calories (approx.) |
|---|---|---|---|
| 🍺 Regular beer | 5% | 355 ml (12 oz) | 150 kcal |
| 🍺 Light beer | 3.5% | 500 ml (16 oz) | 110 kcal |
| 🍷 Wine | 12% | 150 ml (5 oz) | 125 kcal |
| 🍾 Champagne | 11% | 150 ml (5 oz) | 95 kcal |
| 🥃 Spirits (vodka, whiskey, gin) | 40% | 44 ml (1.5 oz) | 97 kcal |
| 🍹 Cocktail | ~15% | varies | 150–300 kcal |
| 🥂 Fortified wine | 16% | 90 ml (3 oz) | 130 kcal |
Legal disclaimer: This calculator is for informational and educational purposes only. Results are approximate estimates and should not be used to determine whether it is safe to drive or operate machinery. Actual BAC depends on many personal factors. If in doubt, do not drink and drive. Always follow the laws of your jurisdiction.
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