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 is blood alcohol content calculated?
BAC is estimated using the Widmark formula: BAC = (A / (r × W)) − (β × t), where A is grams of alcohol consumed, r is the Widmark factor (0.68 for men, 0.55 for women — reflecting lower body water in women), W is body weight in kilograms, β is the elimination rate (0.15 ‰/hour), and t is hours since the first drink. Alcohol grams = volume (ml) × ABV × 0.789 (ethanol density).
What BAC level causes impairment?
Impairment begins at very low levels. At 0.2–0.3 ‰ reaction time is slightly slower and mood lifts. At 0.5 ‰ coordination is noticeably affected and judgment is compromised even if you feel fine. At 1.0 ‰ balance and speech are clearly impaired. At 1.5 ‰ disorientation and nausea are common. Above 3.0 ‰ there is serious risk of alcohol poisoning. European driving limits of 0.2–0.5 ‰ reflect the threshold where crash risk rises significantly.
What are some 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.
Can anything speed up alcohol elimination?
No. The liver eliminates alcohol at a fixed rate of approximately 0.15 ‰ per hour. Coffee, cold showers, energy drinks, and water do not speed up this process. Only time lowers your BAC. If you have a BAC of 0.5 ‰, you need roughly 3–4 hours for it to reach zero regardless of what you do. For general wellness, our sleep cycle calculator helps plan rest after a late night, and our TDEE calculator can support healthy lifestyle habits.