BAC Calculator
Estimate your blood alcohol content using the Widmark formula.
Each standard drink contains ~14g of pure alcohol
BAC Impairment Reference
| BAC Range | Typical Effects |
|---|---|
| 0.00 - 0.02% | No apparent effects; normal behavior |
| 0.02 - 0.05% | Mild relaxation; slight lightheadedness |
| 0.05 - 0.08% | Lowered inhibitions; impaired judgment begins |
| 0.08 - 0.10% | Legally impaired; reduced coordination and reaction time |
| 0.10 - 0.15% | Significant impairment; slurred speech; poor balance |
| 0.15 - 0.25% | Severe impairment; potential blackout; high injury risk |
| 0.25 - 0.40% | Dangerous; risk of alcohol poisoning; medical emergency |
Important: This is an estimate only. Actual BAC varies based on food intake, metabolism, medications, and individual physiology. Never drive after drinking. If in doubt, do not drive. Call a rideshare or designated driver.
Understanding Blood Alcohol Content (BAC)
Blood Alcohol Content, or BAC, is a measurement of the amount of alcohol present 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. BAC is the standard metric used by law enforcement, medical professionals, and researchers to quantify intoxication levels. Understanding how BAC works helps individuals make informed decisions about drinking and driving, recognize the signs of dangerous intoxication, and appreciate how even small amounts of alcohol can impair judgment and motor skills.
The Widmark Formula Explained
The calculator above uses the Widmark formula, one of the most widely accepted methods for estimating BAC. Developed by Swedish researcher Erik Widmark in the 1930s, the formula calculates BAC based on the total grams of alcohol consumed, the drinker's body weight, a gender-based distribution ratio, and the time elapsed since drinking began. The body eliminates alcohol at a relatively constant rate of approximately 0.015% BAC per hour, regardless of body size or how much was consumed. This elimination rate means that if you reach a BAC of 0.15%, it would take roughly 10 hours for your body to process all of the alcohol and return to 0.00%.
Key BAC Facts at a Glance
One standard drink contains approximately 14 grams of pure alcohol (12 oz beer at 5%, 5 oz wine at 12%, or 1.5 oz spirits at 40%).
Elimination rate: The body processes about 0.015% BAC per hour on average.
Legal limit in all 50 US states: 0.08% BAC for drivers 21 and older. Many countries use 0.05% or lower.
Commercial drivers: The federal limit is 0.04% BAC.
Under 21: Zero tolerance laws in most states mean any detectable BAC is illegal.
How Body Weight and Gender Affect BAC
Body weight and biological sex are two of the most significant factors influencing BAC. A person who weighs more has a larger volume of blood and body water to dilute the alcohol, resulting in a lower BAC from the same number of drinks. Gender plays a role through body composition differences: males typically have a higher percentage of body water (approximately 58%) compared to females (approximately 49%). Since alcohol distributes primarily through body water, women generally reach a higher BAC than men of the same weight after consuming an identical amount of alcohol. The Widmark formula accounts for this through gender-specific distribution constants of 0.73 for males and 0.66 for females. Other factors not captured by the formula, including food intake, individual metabolism, medications, fatigue, and liver health, can also significantly influence actual BAC levels.
How Long Alcohol Stays in Your System
While BAC measures the alcohol currently in your bloodstream, alcohol can be detected through various testing methods for different durations. Breath tests can detect alcohol for up to 24 hours after your last drink. Urine tests may detect alcohol metabolites for 12 to 48 hours, and advanced urine tests measuring ethyl glucuronide (EtG) can detect traces for up to 80 hours. Hair follicle tests can show alcohol use for up to 90 days. However, the most relevant measure for impairment remains BAC, since cognitive and motor function are directly tied to the current concentration of alcohol in the blood. Coffee, cold showers, and exercise do not speed up alcohol metabolism. Only time allows the liver to process and eliminate alcohol from the body. The safest approach after any amount of drinking is to arrange alternative transportation rather than attempting to estimate whether you are below the legal limit.