What is blood alcohol content (BAC)?
Blood alcohol content (BAC), measured in promille (‰), indicates the amount of alcohol in your bloodstream. One promille means one gram of pure alcohol per liter of blood. BAC is influenced by the amount of alcohol consumed, body weight, sex, and the time elapsed since drinking. It is the standard measure used to determine legal driving limits across Europe.
How to calculate blood alcohol content?
BAC is calculated using the Widmark formula: BAC = (alcohol in grams / (body weight × Widmark factor)) − (elimination rate × hours). The Widmark factor is 0.68 for men and 0.55 for women. The body eliminates approximately 0.15 ‰ per hour on average.
What is the Widmark formula?
The Widmark formula is: BAC = (A / (r × W)) − (β × t), where A is the mass of alcohol consumed in grams, r is the Widmark factor (0.68 for men, 0.55 for women), W is body weight in kilograms, β is the elimination rate (0.15 ‰/hour), and t is time in hours since the first drink.
BAC calculation examples
An 80 kg man drinking 2 beers (500 ml each, 5% alcohol): alcohol grams = 2 × 500 × 0.05 × 0.789 = 39.45 g. BAC = 39.45 / (0.68 × 80) = 0.73 ‰. After 2 hours: 0.73 − 0.30 = 0.43 ‰.
A 60 kg woman drinking 2 glasses of wine (150 ml each, 12%): alcohol grams = 2 × 150 × 0.12 × 0.789 = 28.4 g. BAC = 28.4 / (0.55 × 60) = 0.86 ‰.
What are the legal BAC limits for driving?
Legal BAC limits vary by country. In Lithuania the limit is 0.4 ‰ for experienced drivers (0.0 ‰ for novice drivers). In Norway the limit is 0.2 ‰. Exceeding these limits can result in fines, license suspension, and criminal charges.
What factors affect blood alcohol content?
Many factors influence BAC including body weight, sex, food consumption, drinking speed, overall health, and liver function. Women generally reach higher BAC levels than men at the same consumption level because their bodies contain less water relative to body mass.