Estimate your blood alcohol content based on what you drank, your body weight, gender, and how much time has passed. Add each drink individually for the most accurate reading — your BAC updates in real time.
Pro tip: A “standard drink” is 14 grams of pure alcohol — that’s 12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% spirits. Most restaurant pours exceed these sizes significantly.
How BAC Is Calculated: The Widmark Formula Explained
The Widmark formula is the standard method forensic toxicologists use to estimate blood alcohol content. The equation is BAC = (A / (W × r)) − (β × t), where A is total grams of alcohol consumed, W is body weight in grams, r is the Widmark factor (0.68 for males, 0.55 for females), β is the elimination rate (approximately 0.015 per hour), and t is hours since drinking began. The gender-based factor accounts for differences in body water composition — males typically have more body water, which dilutes alcohol more effectively. The elimination rate of 0.015 represents average liver metabolism of ethanol via alcohol dehydrogenase, though this ranges from 0.010 to 0.020 depending on genetics, liver health, and drinking history. Each drink is converted to grams of pure alcohol using grams = oz × (ABV/100) × 29.5735 × 0.789, where 29.5735 converts fluid ounces to millilitres and 0.789 is the density of ethanol.
What Is a Standard Drink? (With Size Comparisons)
A standard drink in the United States contains exactly 14 grams of pure ethanol — roughly 12 fluid ounces of 5% beer, 5 fluid ounces of 12% wine, or 1.5 fluid ounces of 40% spirits. These different serving sizes all deliver the same amount of alcohol to your bloodstream. Real-world pours rarely match these benchmarks: craft beers range from 6% to 12% ABV, meaning a single pint can equal two or three standard drinks. A generous restaurant wine pour of 8 ounces at 14% ABV is nearly double a standard drink, and cocktails like a Long Island Iced Tea can contain four standard drinks in one glass. When using this calculator, enter the actual size and ABV of each drink. The standard drink count in the results helps contextualize consumption relative to public health guidelines, which recommend no more than two per day for men and one for women.
BAC Levels and Their Effects on the Body
At 0.01–0.03 BAC, most people feel normal with only subtle mood changes. Between 0.04–0.06, warmth, relaxation, and minor reasoning impairment begin, with lowered inhibitions. At 0.07–0.09, balance, speech, reaction time, and hearing are noticeably impaired — this is why most US states set the legal limit at 0.08. Between 0.10–0.14, motor control deteriorates sharply and slurred speech becomes obvious. Above 0.15, most people experience vomiting, major balance loss, and potential blackouts. A BAC exceeding 0.30 carries risk of life-threatening alcohol poisoning, loss of consciousness, and suppressed vital functions. These ranges are averages — tolerance, medications, fatigue, and food intake all shift individual thresholds.
How Long Does Alcohol Stay in Your System?
The liver eliminates alcohol at a constant rate of roughly 0.015 BAC per hour regardless of how much you consumed. A BAC of 0.08 takes about 5.3 hours to reach zero, while 0.15 requires roughly 10 hours. No method — coffee, cold showers, exercise, or food — meaningfully speeds this process; they may increase alertness, but BAC remains unchanged. While blood alcohol clears in hours, metabolites persist longer: breath tests stay positive up to 24 hours, urine tests 48 to 80 hours, and hair follicle tests up to 90 days. If you plan to drive, use the “Time to 0.00” result as a minimum waiting period and always add a safety buffer. Next-day studies show measurable cognitive deficits even after BAC returns to zero following heavy sessions.
Factors That Affect Your BAC Beyond Weight and Gender
While the Widmark formula accounts for body weight and biological sex, many other variables influence actual BAC. Food intake can reduce peak BAC by up to 20% by slowing gastric emptying. Body composition matters because fat tissue contains less water than muscle, so two people of equal weight but different body fat percentages reach different BAC levels. Genetics create variations in alcohol dehydrogenase enzymes — some populations metabolize alcohol faster or slower. Medications including antihistamines and antidepressants can amplify effects without changing BAC. Hydration, fatigue, and rate of consumption all alter absorption speed and effect intensity. Older adults typically have lower body water content and slower metabolism, leading to higher BAC from the same intake. This calculator provides a useful estimate, but individual results always vary.
Looking for related tools? Try our Body Fat Calculator to understand your body composition, or explore all Health & Fitness tools.