BAC Calculator

About This Tool

Blood Alcohol Content (BAC) measures the concentration of alcohol in your bloodstream, expressed as a percentage by weight. A BAC of 0.08% means there are 0.08 grams of alcohol per 100 milliliters of blood. This metric is used worldwide for legal purposes (driving limits) and medical purposes (assessing intoxication level). The legal BAC limit for driving is 0.08% in all 50 US states, 0.05% in most European and Australian jurisdictions, and 0.00% in some countries including Saudi Arabia, the UAE, and Hungary.

This calculator uses the Widmark formula, developed by Swedish scientist Erik Widmark in the 1930s and still the most widely used method for estimating BAC from known alcohol consumption. The formula accounts for the amount of alcohol consumed, body weight, biological sex (which affects body water ratio), and time elapsed since drinking began. While no formula can precisely predict BAC for every individual — absorption rates, metabolism, food intake, and genetics all vary — the Widmark formula provides a clinically validated estimate.

The Widmark Formula Explained

The formula calculates BAC as: (ounces of alcohol consumed × 5.14) / (body weight in pounds × Widmark r factor) − (0.015 × hours since drinking). The constant 5.14 converts ounces of alcohol into a BAC-compatible unit. The Widmark r factor accounts for the proportion of body mass in which alcohol distributes — 0.68 for males and 0.55 for females. Women have a lower r factor because they typically have a higher percentage of body fat (which does not absorb alcohol) and lower percentage of body water. The 0.015 per hour represents the average rate at which the liver metabolizes alcohol, which is relatively constant regardless of how much you drink.

What Is a Standard Drink?

In the United States, one standard drink contains approximately 0.6 fluid ounces (14 grams) of pure alcohol. This equals 12 ounces of regular beer (5% ABV), 5 ounces of wine (12% ABV), or 1.5 ounces of distilled spirits (40% ABV / 80 proof). Craft beers, wines, and cocktails often exceed these standard amounts — a 16-oz pint of an 8% IPA contains about 1.6 standard drinks, and a generous pour of wine at a restaurant may be 7-8 ounces (1.4-1.6 standard drinks). Underestimating drink count is one of the biggest sources of error in BAC estimation.

Factors That Affect BAC

Several factors beyond weight and sex influence actual BAC. Food in the stomach slows alcohol absorption significantly — drinking on a full stomach can reduce peak BAC by 20-30% compared to drinking on an empty stomach. Carbonated beverages (beer, sparkling wine, mixers like tonic) accelerate absorption. Medications including antihistamines, antidepressants, and pain relievers can amplify alcohol's effects without changing BAC. Age affects metabolism — older adults generally reach higher BAC levels from the same number of drinks due to decreased body water and slower metabolism. Genetic variations in alcohol dehydrogenase (the enzyme that breaks down alcohol) cause significant individual differences in how quickly alcohol is processed.

Impairment at Different BAC Levels

At 0.02-0.03% BAC, most people experience slight mood elevation and relaxation with minimal cognitive impairment. At 0.04-0.06%, inhibitions are lowered, reaction time slows, and fine motor skills begin to decline. At 0.08% — the legal limit — significant impairment in balance, speech, vision, reaction time, and judgment is present. At 0.15%, most people experience significant motor impairment and may vomit or black out. At 0.20-0.25%, confusion, disorientation, and inability to stand or walk unassisted are common. At 0.30%, loss of consciousness is likely. At 0.40% and above, the risk of death from respiratory depression is significant — this is the LD50 (lethal dose for 50% of people) for alcohol.

Sobering Up: What Actually Works

The only thing that reduces BAC is time. Coffee, cold showers, exercise, and food do not accelerate alcohol metabolism — your liver processes alcohol at a fixed rate of approximately 0.015% BAC per hour (about one standard drink per hour). This means if your peak BAC reaches 0.12%, it will take approximately 8 hours to return to 0.00%. There is no shortcut. The common belief that coffee sobers you up is dangerous — caffeine may make you feel more alert while your coordination and judgment remain impaired. The safest approach is to plan ahead: designate a sober driver, use rideshare services, or limit consumption to a rate your body can metabolize.