Blood Alcohol Content (BAC) Calculator

What is Blood Alcohol Content (BAC)?

Blood Alcohol Content (BAC) is a measurement of the percentage of alcohol in a person's bloodstream. A BAC of 0.10% means that there is 1 part alcohol for every 1,000 parts blood. This metric is the standard used by law enforcement to determine whether a person is legally impaired. Even small amounts of alcohol can affect your judgment, coordination, and reaction time. This BAC calculator uses the Widmark formula to provide an estimate of your BAC, helping you make more informed and safer decisions after drinking.

How BAC is Calculated: The Widmark Formula

This calculator estimates BAC using the Widmark formula, a scientifically accepted method for this purpose. The formula is:

• Alcohol in Grams: A "standard drink" in the U.S. (e.g., 12 oz beer, 5 oz wine, 1.5 oz spirits) contains about 14 grams of alcohol.
• Body Weight: A person's weight determines the volume of water in their body, which affects how alcohol is diluted.
• 'r' (Gender Constant): This is the water distribution ratio in the body, which is different for men (0.68) and women (0.55) on average.
• Time: The body metabolizes alcohol at a relatively constant rate of about 0.015% per hour.

Factors That Influence BAC

The Widmark formula provides a great estimate, but real-world BAC can be affected by several other factors:

• Food: Eating food before or while drinking slows the absorption of alcohol into the bloodstream.
• Body Composition: Since alcohol is not absorbed into fat tissue, a person with a higher body fat percentage may have a higher BAC than a leaner person of the same weight. You can estimate your body composition with our Lean Body Mass Calculator.
• Medications & Health: Certain medications and health conditions can affect how your body metabolizes alcohol.

The Dangers of Impaired Driving

It's critical to understand that even a low BAC can impair driving ability. In all 50 U.S. states, it is illegal to drive with a BAC of 0.08% or higher. However, impairment can begin at much lower levels. Making the choice to not drink and drive is the only way to guarantee safety. The journey to responsible habits is a day-by-day process, similar to the one tracked by our Sobriety Calculator. For more information on the effects of alcohol, the National Institute on Alcohol Abuse and Alcoholism (NIAAA) is a leading resource.