Blood Alcohol Calculator

BAC = (alcohol_grams × 0.806) / (body_weight_kg × r) - (elimination_rate × hours_since_drinking). Where r is the "body water" factor: ~0.68 for men, ~0.55 for women (women have more body fat per kg, less water to dilute alcohol). Elimination rate is typically 0.015% per hour but varies by individual (0.012 to 0.020).

Standard "alcohol grams" per drink: 0.5L of 5% beer = 20g; 100ml of 12% wine = 9.6g; 30ml of 40% vodka = 9.6g. The "one drink = one drink" rule is roughly right for these standard sizes; bigger pours or stronger drinks = more alcohol.

• Food in stomach — slows absorption significantly. Drinking on empty stomach produces 30-50% higher peak BAC than the same alcohol with food.
• Drink type — carbonated drinks (champagne, beer) absorb faster than still wine; spirits absorb fastest.
• Individual elimination rate — varies 30%+ between healthy adults. Older adults metabolize slower; chronic heavy drinkers may metabolize slightly faster (tolerance is mostly nervous system, not metabolic).
• Medications — many drugs interact with alcohol or its metabolism. Acetaminophen + alcohol is liver-toxic; sedatives + alcohol is dangerously additive.
• Genetic variation — about 30% of East Asians have a variant of ALDH2 that slows acetaldehyde metabolism — "Asian flush" plus higher BAC for the same drinks.
• Hydration status, body temperature, fatigue — all modulate BAC slightly.

• 0.02-0.03% — mild effects. Slight relaxation.
• 0.04-0.06% — buzz. Some inhibition reduction; mild reaction-time loss.
• 0.07-0.09% — noticeable impairment. Most legal driving limits cross here.
• 0.10-0.12% — clearly drunk. Significant motor coordination loss, slurred speech.
• 0.13-0.15% — staggering, slurring obvious to onlookers.
• 0.18-0.25% — heavy intoxication. Risk of blackout (memory loss).
• 0.25-0.35% — stupor, possible loss of consciousness.
• 0.35%+ — life-threatening. Alcohol poisoning. ER visit needed.
• 0.40%+ — coma, death risk significant. LD50 for adults is ~0.40-0.50%.

• You are curious about how many drinks affects your specific BAC — for awareness, not for "is it safe to drive".
• You are calculating "how long until I can drive" after a social event (with the caveat that this is an estimate, not a guarantee).
• You are explaining alcohol effects to a friend or younger family member with concrete numbers.
• You are learning about alcohol metabolism for educational reasons.

• It will not measure actual BAC. Real measurement requires a breathalyzer (~$30 consumer / certified $200+) or blood draw. The calculation is a prediction; actual values vary ±20-30%.
• It will not tell you when it is "safe to drive". The only safe BAC for driving is 0.00%. Any alcohol impairs reaction time, even below legal limits.
• It will not work for very heavy drinking or alcohol poisoning. Above 0.30% BAC, individual variation is huge and any prediction is unreliable. Above 0.35%, seek medical help.
• It will not account for medications, illness, or recent food. The formula's assumptions are "average adult, fasting, no medication" — your situation may differ significantly.