BAC Calculator — Blood Alcohol Content Estimator

Estimate your blood alcohol content using the Widmark formula. For entertainment purposes only. Never drink and drive.

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For entertainment purposes only. Never drink and drive. This tool does not provide legal or medical advice. Actual impairment varies significantly by individual.

Fill in the form to estimate your blood alcohol content.

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How BAC Is Calculated — The Widmark Formula

Blood alcohol content (BAC) is a measure of the concentration of alcohol in a person's bloodstream, expressed as a percentage. A BAC of 0.08% means there are 0.08 grams of alcohol per 100 millilitres of blood. BAC is the standard legal measure of alcohol intoxication used by law enforcement and courts in most countries worldwide.

The most widely used method for estimating BAC is the Widmark formula, developed by Swedish physician Erik Widmark in the 1930s. The formula calculates BAC based on the amount of alcohol consumed, the person's body weight, their biological sex (which affects body water percentage), and the time elapsed since drinking began (because the liver metabolises alcohol at a roughly constant rate).

The formula works as follows: first, calculate the total grams of pure alcohol consumed. Pure alcohol has a density of approximately 0.789 g/mL. For each drink, multiply the volume in mL by the ABV percentage by 0.789 to get grams. Then, divide the total grams by the person's body weight in kilograms multiplied by the Widmark factor (r) and 1000, then multiply by 100 to get a percentage. Finally, subtract the alcohol already metabolised: the liver processes approximately 0.015% BAC per hour, so multiply 0.015 by the hours elapsed and subtract from the raw BAC figure.

Widmark Factor: Why Gender Matters

The Widmark factor (r) represents the proportion of body weight made up of body water, since alcohol distributes throughout total body water. Men typically have a higher percentage of lean muscle mass and total body water than women of the same weight, meaning the same amount of alcohol is diluted across a larger water volume in men. The standard Widmark factor is 0.68 for males and 0.55 for females, though these are averages — body composition, age, fitness level, and individual variation all affect the actual distribution.

This is why, all else being equal, women typically reach higher BAC levels than men after consuming the same number of drinks: the alcohol is distributed across a smaller volume of body water. Additionally, women have lower levels of the enzyme alcohol dehydrogenase in the stomach lining, meaning less alcohol is broken down before it reaches the bloodstream.

Factors Affecting BAC Beyond the Widmark Formula

The Widmark formula provides an estimate based on physical factors, but many other variables affect real-world BAC and perceived intoxication. Food consumption significantly slows alcohol absorption — drinking on an empty stomach results in a faster, higher peak BAC than drinking with food. Drinking pace affects the peak BAC; rapid consumption leads to higher peaks before metabolism can begin reducing the level. Carbonation in sparkling wine and mixers may accelerate alcohol absorption slightly. Medications can interact dangerously with alcohol — antihistamines, sedatives, and certain antibiotics amplify alcohol's effects. Tolerance affects perceived impairment but not actual BAC: a person with high alcohol tolerance will feel less impaired at the same BAC but is equally legally impaired and equally dangerous behind the wheel.

Individual variation in alcohol metabolism is also significant. The liver's average metabolism rate of 0.015% BAC per hour is an estimate; actual rates vary from about 0.010% to 0.020% per hour depending on genetics, liver health, body size, and drinking history. Body composition matters too: a muscular person and an obese person of the same total weight may have very different BAC levels because muscle contains more water than fat.

Legal Limits Around the World

The most common legal BAC limit for driving is 0.08% (80 mg/100 mL), used in the United States, United Kingdom, Canada, and many other countries. However, many jurisdictions are stricter. Australia and mainland Europe set the limit at 0.05%. Sweden, Japan, and several Eastern European and Asian countries use 0.02%. Saudi Arabia, the UAE, India (in some states), and other countries have zero-tolerance policies with a 0.00% legal limit. For commercial drivers and under-21 drivers, limits are typically much lower — often 0.02% or 0.04% even in countries with a general 0.08% limit.

It is critical to understand that these limits describe legal thresholds, not safety thresholds. Impairment begins at BAC levels as low as 0.02%, and reaction times and decision-making are measurably degraded well below the legal limit. The only safe BAC for driving is 0.00%.

Frequently Asked Questions

This calculator provides a mathematical estimate based on the Widmark formula. It is for entertainment and educational purposes only. Real BAC varies due to factors the formula cannot capture, including food consumption, drinking pace, medications, individual metabolism variation, and body composition. Do not use this calculator to decide whether it is safe to drive. The only reliable way to measure BAC is with a certified breathalyser or blood test.

At the average metabolism rate of 0.015% per hour, divide your peak BAC by 0.015 to get the approximate number of hours until sober. For example, a peak BAC of 0.09% takes about 6 hours to metabolise. Nothing speeds up alcohol metabolism — not coffee, food, cold showers, or exercise. Only time works. The calculator shows a "time until sober" estimate based on this formula.

In the US, one standard drink contains 14 grams of pure alcohol. This equals: 12 fl oz of regular beer (5% ABV), 5 fl oz of wine (12% ABV), or 1.5 fl oz of distilled spirits (40% ABV). In the UK, one unit equals 10 mL (8 grams) of pure alcohol. Craft beers (often 7-9% ABV), large wine pours, and double spirits count as more than one standard drink, which is why it is important to account for actual ABV when estimating BAC.

Food slows the rate of alcohol absorption but does not reduce the total amount of alcohol that enters your bloodstream. Eating before or during drinking delays the peak BAC and makes the rise more gradual — potentially keeping peak BAC lower — but the same total amount of alcohol will eventually be absorbed. Food does not "soak up" alcohol that has already been absorbed. Once alcohol is in the bloodstream, only metabolism over time reduces BAC.

Legal limits are set by governments based on a combination of research evidence, lobbying, cultural norms, and public health goals. Research consistently shows impairment begins well below 0.08%, and many road safety researchers and public health bodies recommend the 0.05% limit as a better evidence-based threshold. Countries that lowered their limit from 0.08% to 0.05% (such as Australia in the 1970s and Scotland in 2014) have seen measurable reductions in alcohol-related crashes. The US 0.08% limit was set in 2000, replacing a patchwork of state limits, and there is ongoing debate about whether it should be lowered.

Tolerance affects the perception of intoxication but not actual BAC. A heavy drinker with high tolerance may feel relatively sober at 0.12% BAC while a light drinker feels severely impaired at 0.05% — but both have the same cognitive and motor impairment as measured objectively. This is a particularly dangerous aspect of tolerance: people may believe they are safe to drive because they feel fine, while their actual driving ability is significantly compromised. BAC remains the standard legal measure precisely because it is objective.

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