BAC Calculator
Estimate your Blood Alcohol Content (BAC) using the Widmark formula. Enter your weight, sex, number of drinks, and time elapsed for an approximate BAC level.
Important Safety Warning
This calculator provides a rough mathematical estimate only. Actual BAC varies significantly based on food intake, metabolism, medications, health conditions, and many other factors. Never use this tool to determine whether it is safe to drive or operate machinery. The only safe amount of alcohol before driving is zero. If you have been drinking, use a designated driver, rideshare, or taxi.
Quick Answer
BAC is estimated using the Widmark formula: BAC = (Alcohol oz x 5.14) / (Body Weight lbs x Widmark r) - (0.015 x Hours). The Widmark r factor is 0.73 for males and 0.66 for females. One standard drink contains approximately 0.6 oz of pure alcohol. The body eliminates alcohol at roughly 0.015% per hour.
Affects the Widmark distribution factor (r = 0.73 male, 0.66 female)
Each standard drink contains ~0.6 oz of pure alcohol
Estimated Results
What This Means
Lowered inhibitions, slight euphoria, relaxation
Legal status: Below the standard legal limit, but impairment may still occur
BAC Levels and Effects
Legal BAC Limits by Region
About This Tool
The BAC (Blood Alcohol Content) Calculator uses the Widmark formula, one of the oldest and most widely referenced methods for estimating blood alcohol concentration. Developed by Swedish physician Erik Widmark in the 1930s, this formula provides a mathematical approximation of the amount of alcohol in a person's bloodstream based on their body weight, biological sex, the amount of alcohol consumed, and the time elapsed since drinking. While modern pharmacokinetic models have become more sophisticated, the Widmark formula remains the foundation of BAC estimation and is widely used in forensic toxicology, law enforcement, and educational settings.
How the Widmark Formula Works
The Widmark formula calculates BAC as: BAC = (A x 5.14) / (W x r) - (0.015 x H), where A is the total ounces of pure alcohol consumed, W is body weight in pounds, r is the Widmark distribution factor (0.73 for males, 0.66 for females), H is hours since the first drink, and 0.015 is the average alcohol elimination rate per hour. The constant 5.14 converts ounces of alcohol to a form compatible with pounds of body weight. The distribution factor (r) accounts for differences in body water content between sexes; since alcohol distributes in body water, individuals with higher water content (typically males) will have a lower BAC from the same amount of alcohol.
What Is a Standard Drink?
In the United States, a standard drink is defined as any beverage containing approximately 0.6 fluid ounces (14 grams) of pure alcohol. This corresponds to 12 ounces of regular beer (5% ABV), 5 ounces of wine (12% ABV), or 1.5 ounces of distilled spirits (40% ABV or 80 proof). It is critically important to understand that many common servings exceed these standard amounts. A typical restaurant pour of wine is often 6-8 ounces. Craft beers frequently range from 6-12% ABV. Mixed cocktails may contain 2-3 standard drinks worth of alcohol. Failing to account for non-standard serving sizes is one of the most common reasons people underestimate their BAC.
Factors That Affect Actual BAC
The Widmark formula provides a simplified estimate and cannot account for the many physiological factors that influence actual BAC. Food in the stomach significantly slows alcohol absorption, which is why drinking on an empty stomach leads to faster intoxication. The rate of drinking matters enormously; consuming four drinks in one hour produces a much higher peak BAC than consuming four drinks over four hours. Individual metabolism varies widely based on genetics, liver health, enzyme activity (particularly alcohol dehydrogenase and aldehyde dehydrogenase), age, and regular alcohol consumption patterns. Medications, particularly those metabolized by the liver, can interact with alcohol and alter both its effects and elimination rate. Body composition matters beyond simple weight; a muscular person and an obese person of the same weight will have different BACs because muscle tissue contains more water than fat tissue.
Alcohol Elimination and Sobering Up
The human body eliminates alcohol at a relatively constant rate of approximately 0.015% BAC per hour, though this can range from 0.010% to 0.020% between individuals. This means a person with a BAC of 0.08% would take roughly 5.3 hours to fully eliminate all alcohol from their system. There is no way to speed up this process. Coffee, cold showers, exercise, and food do not accelerate alcohol metabolism. They may make a person feel more alert, but they do not lower BAC. The only thing that reduces BAC is time. This is an important public health point: a person who stops drinking at 2:00 AM after reaching a BAC of 0.15% may still be legally impaired at 8:00 AM the next morning.
Legal Implications
Most US states set the legal driving limit at 0.08% BAC, though Utah lowered its limit to 0.05% in 2018. Commercial vehicle operators face a stricter 0.04% limit federally. Drivers under 21 are subject to zero-tolerance laws in most states, with limits typically at 0.00% or 0.02%. Internationally, many countries have adopted 0.05% or lower limits, and some countries enforce complete zero-tolerance policies. It is essential to understand that impairment begins well below the legal limit. Research consistently shows that reaction time, judgment, and coordination are measurably impaired at BAC levels as low as 0.02%, and the risk of a fatal crash doubles at 0.05% BAC compared to 0.00%.