Estimate your Blood Alcohol Concentration (BAC) using the Widmark formula. See how long until your BAC returns to zero and understand impairment levels.
The Alcohol BAC Estimator Calculator uses the Widmark formula to estimate your Blood Alcohol Concentration based on the number of standard drinks consumed, your body weight, sex, and time elapsed. BAC is expressed as grams of alcohol per 100 mL of blood (e.g., 0.08 g/dL is the legal driving limit in most U.S. states).
The Widmark formula is the most widely used BAC estimation method in forensic toxicology and provides a reasonable approximation. However, actual BAC varies based on many factors including food intake, metabolism rate, hydration status, medications, and individual liver enzyme activity.
This calculator is strictly for educational purposes. It must NOT be used to determine fitness to drive, operate machinery, or make legal decisions. When in doubt, do not drive. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process.
Understanding BAC helps illustrate how quickly alcohol impairs judgment, reaction time, and coordination — often before you "feel drunk." At 0.05 BAC, most people experience reduced inhibition and impaired judgment, while at 0.08 BAC (the legal limit), reaction time, coordination, and reasoning are significantly impaired. This tool makes the math transparent.
Widmark Formula: BAC = (A / (W × r)) − (β × t) where: • A = alcohol consumed in grams = standard drinks × 14 g • W = body weight in grams • r = Widmark factor (0.68 for men, 0.55 for women) • β = elimination rate = 0.015 g/dL per hour • t = hours since first drink 1 US standard drink = 14 g pure alcohol: • 12 oz beer (5% ABV) • 5 oz wine (12% ABV) • 1.5 oz spirits (40% ABV) Time to 0.00 = BAC / 0.015 (hours)
Result: Estimated BAC: 0.063 g/dL
Alcohol = 4 × 14 = 56 grams. Weight = 180 lbs = 81,647 grams. BAC = (56 / (81647 × 0.68)) − (0.015 × 2) = 0.001009 × 1000 − 0.030 ≈ 0.063 g/dL. This is below the 0.08 legal limit but still causes impairment. Time to 0.00 = 0.063 / 0.015 ≈ 4.2 hours from now.
Alcohol impairment begins at very low BAC levels. At 0.02, mood is slightly elevated and judgment begins to decline. By 0.05, inhibitions are lowered and reaction time is measurably slower. At 0.08 (the legal limit), muscle coordination, balance, and reasoning are significantly impaired. Beyond 0.15, gross motor control is seriously compromised, and BAC above 0.30 can cause loss of consciousness or death.
The legal BAC limit for driving varies globally: 0.08 (U.S., UK, Canada), 0.05 (most of Europe, Australia), 0.03 (Japan, India, many South American countries), and 0.00 (Czech Republic, Hungary, Romania for all drivers). Many jurisdictions have lower limits for commercial drivers (0.04) and zero tolerance for drivers under 21.
Beyond acute impairment, regular alcohol consumption at even moderate levels increases risk for certain cancers, liver disease, cardiovascular issues, and neural damage. Recent large-scale studies suggest there is no safe level of alcohol consumption from a health perspective, though individual risk depends on genetic factors, consumption patterns, and overall health.
Absolutely NOT. This calculator provides rough estimates only. Actual BAC depends on many factors this formula cannot capture: food intake, hydration, medications, liver function, and individual variation. Impairment begins well below the legal limit. If you've been drinking at all, use a ride service or designated driver.
In the U.S., one standard drink contains 14 grams of pure alcohol. This equals approximately 12 oz of regular beer (5% ABV), 5 oz of wine (12% ABV), or 1.5 oz of distilled spirits (40% ABV/80 proof). Many beers, wines, and cocktails contain significantly more than one standard drink per serving.
The Widmark r factor represents the fraction of body weight that is water (since alcohol distributes into body water). Men average r = 0.68 and women r = 0.55 because women generally have a higher proportion of body fat and lower body water percentage. This means the same amount of alcohol produces a higher BAC in women.
The average elimination rate is 0.015 g/dL per hour (sometimes cited as 0.015–0.020). This is primarily determined by liver enzyme (alcohol dehydrogenase) capacity and is relatively constant regardless of BAC level. Heavy chronic drinkers may have slightly faster elimination rates due to enzyme induction.
Yes. Alcohol does not distribute into fat tissue, only into body water. Two people weighing the same but with different body fat percentages will have different BACs from the same amount of alcohol. The person with more body fat will have a higher BAC because their effective distribution volume is smaller.
The Widmark formula provides estimates within about ±0.01–0.02 g/dL for most people. It assumes drinking occurred over a short period and doesn't account for absorption kinetics. Real BAC follows a curve: rising during absorption (30–60 minutes after drinking) and falling during elimination. The formula is most accurate during the post-absorption (falling) phase.