Estimate your blood alcohol level with the Widmark Formula
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Blood Alcohol Concentration (BAC) is the gold standard metric used globally by law enforcement, medical professionals, and researchers to measure the level of intoxication in an individual. It represents the percentage of alcohol (ethanol) in your bloodstream. For example, a BAC of 0.10% means that 0.10% of a person's blood volume is comprised of alcohol. While this may sound like a small number, alcohol is a potent substance, and even trace amounts can significantly impair motor skills, judgment, and reaction times.
Our free BAC calculator is designed to provide you with a reliable estimate of your intoxication level. It utilizes the widely accepted Widmark Formula, which takes into account critical variables such as body weight, biological sex, the amount of alcohol consumed, and the time elapsed since drinking began. Understanding your BAC is essential for making safe, informed decisions, though it should never be used to justify driving after drinking.
The Widmark Formula was developed by Swedish scientist Erik Widmark in the 1930s and remains the foundational calculation for forensic toxicology regarding alcohol. While our calculator handles the complex math for you, understanding the underlying science can be helpful.
The core concept calculates the mass of alcohol consumed and divides it by the body mass, adjusted for a "distribution factor" (r). The formula is generally expressed as:
The variable 'r' represents the distribution of water in the body. Alcohol is water-soluble, meaning it disperses into the water in your body but not the fat. Because muscle tissue contains more water than fat tissue, and men generally have a higher muscle-to-fat ratio than women, the 'r' value differs:
This formula explains why a woman often has a higher BAC than a man of the exact same weight who drank the exact same amount of alcohol.
Alcohol affects everyone differently. Two people can share a bottle of wine and end up with vastly different BAC readings. Here are the primary factors that influence how your body processes alcohol:
As mentioned above regarding the Widmark formula, females typically have less body water and more body fat than males. Additionally, women have lower levels of *alcohol dehydrogenase*, the enzyme in the stomach responsible for breaking down alcohol before it reaches the bloodstream. This biological difference means alcohol remains more concentrated in a female's body.
Blood volume typically increases with body weight. A heavier person has more blood and water to dilute the alcohol they consume, resulting in a lower BAC compared to a lighter person drinking the same amount. However, this relies on the weight being lean muscle mass; high body fat does not help dilute alcohol as effectively because fat does not absorb alcohol.
The faster you drink, the higher your peak BAC will be. The liver can only metabolize approximately one standard drink per hour (or 0.015% BAC per hour). If you consume three drinks in one hour, your BAC will spike because the alcohol accumulates in your blood faster than your liver can eliminate it.
The phrase "don't drink on an empty stomach" is scientifically sound advice. When there is food in your stomach, the pyloric valve (which connects the stomach to the small intestine) closes to digest the food. This keeps the alcohol in the stomach longer, where absorption is slower. On an empty stomach, the pyloric valve is open, allowing alcohol to rush immediately into the small intestine, where it is absorbed into the bloodstream almost instantly.
Many medications react adversely with alcohol. Drugs like Tylenol (acetaminophen) can cause liver damage when mixed with alcohol. Others, such as antidepressants, anti-anxiety meds (Xanax, Valium), and allergy medications (Benadryl), can amplify the intoxicating effects of alcohol, making you feel much "drunker" than your BAC would suggest.
Not all drinks are created equal. A craft beer with 9% ABV (Alcohol By Volume) will raise your BAC almost twice as fast as a standard light beer with 4.2% ABV. Similarly, "pint" glasses at bars can vary from 16oz to 20oz. Our calculator allows you to customize these inputs for accuracy.
While fatigue and dehydration do not technically change the BAC *number* significantly, they drastically alter how you *feel* and impair your cognitive abilities. A tired driver with a BAC of 0.05% may be just as dangerous as a well-rested driver with a BAC of 0.08%.
To accurately estimate your BAC, you must count standard drinks, not just the physical number of glasses or cans. In the United States, a standard drink contains roughly 14 grams of pure alcohol.
Alcohol is a depressant that affects the central nervous system. As your BAC rises, you will pass through predictable stages of impairment:
One of the most persistent myths is that you can "sober up" quickly. This is false.
Alcohol metabolism follows "Zero-Order Kinetics," meaning the liver processes alcohol at a constant rate, regardless of how much you have drunk. For the average human, this rate is approximately 0.015 grams/100mL/hour (or 0.015% BAC drop per hour).
If your BAC reaches 0.15% (roughly twice the legal limit), it will take approximately 10 hours for the alcohol to completely leave your system.
Driving under the influence is a serious crime that endangers lives.