How many drinks does it take to reach the legal limit? When are you sober enough to drive? The Widmark formula estimates your blood alcohol concentration (BAC) based on drink volume, alcohol content, body weight and gender.
This guide explains the calculation, how your body eliminates alcohol, and the key legal limits.
The Widmark Formula
Developed by Erik Widmark in 1932, this formula calculates blood alcohol concentration (BAC) in per mille (‰):
Alcohol (g) = Volume (ml) × (ABV / 100) × 0.8
BAC (‰) = Alcohol (g) / (Body weight (kg) × r)
r = 0.68 (men) | r = 0.55 (women)
The reduction factor r accounts for different body water ratios. Women have a lower average water content, so alcohol concentrates more.
Example Calculation
| Step | Calculation |
|---|---|
| Drink | 500 ml beer, 5% ABV |
| Alcohol (g) | 500 × 0.05 × 0.8 = 20 g |
| BAC (male, 80 kg) | 20 / (80 × 0.68) = 0.37‰ |
| BAC (female, 60 kg) | 20 / (60 × 0.55) = 0.61‰ |
Alcohol Elimination
Your body eliminates alcohol at a nearly constant rate: approximately 0.15 per mille per hour. This value varies slightly between individuals but is largely independent of body weight or gender.
Current BAC = Initial BAC − (0.15 × hours)
Time until sober = Initial BAC / 0.15
Coffee, cold showers, or exercise do not speed up elimination. Only time helps.
Legal Limits
| Country | BAC Limit |
|---|---|
| Germany | 0.5‰ (0.0‰ for novice drivers) |
| USA | 0.08% BAC (≈ 0.8‰) |
| UK | 0.08% BAC (≈ 0.8‰) |
| Sweden / Poland | 0.2‰ |
| Czech Republic / Hungary | 0.0‰ |
Factors That Affect BAC
Body weight
More body mass distributes alcohol across a larger volume — resulting in a lower BAC.
Gender
Women have a lower body water ratio (55% vs. 68%), leading to a higher BAC from the same amount of alcohol.
Stomach contents
Food slows alcohol absorption but doesn't reduce the total BAC. The peak is simply delayed.
Drinking speed
Faster drinking raises BAC more quickly since elimination can't keep up with absorption.
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Your water needs increase with alcohol consumption. And your daily calorie burn is affected by alcohol — a beer contains about 200 kcal.
Conclusion
The Widmark formula provides a reliable estimate of blood alcohol concentration. But keep in mind: individual factors like medication, liver health, and genetics can influence the result. When in doubt, don't drive. Use our Blood Alcohol Calculator for a personal estimate.
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