What is the Widmark formula?

The Widmark formula estimates blood alcohol content as: BAC = (alcohol consumed in grams / (body weight in grams × Widmark r factor)) × 100 − (0.015 × hours since first drink). The r factor is approximately 0.68 for males and 0.55 for females, reflecting differences in body water content.

What is the legal BAC limit for driving?

In the United States, the legal BAC limit is 0.08% for drivers aged 21 and over in all 50 states. For commercial drivers, the limit is 0.04%. Many states have zero-tolerance laws for drivers under 21, with limits of 0.00% to 0.02%. Some countries have lower limits, such as 0.05% in Australia and much of Europe.

How long does it take for alcohol to leave your system?

The body metabolizes alcohol at a relatively constant rate of approximately 0.015% BAC per hour, which is roughly equivalent to one standard drink per hour for an average-sized person. However, this rate varies by individual based on liver health, genetics, food intake, and other factors. A BAC of 0.08% would take roughly 5.3 hours to reach 0.00%.

What is a standard drink?

In the United States, a standard drink contains about 14 grams (0.6 ounces) of pure alcohol. This is roughly equivalent to 12 ounces of regular beer (5% ABV), 5 ounces of wine (12% ABV), or 1.5 ounces of distilled spirits (40% ABV / 80 proof). Many drinks served at bars and restaurants contain more alcohol than one standard drink.

BAC Calculator

Important Health & Safety Disclaimer

This calculator provides rough estimates only and should NEVER be used to determine if you are safe to drive. Individual BAC varies significantly based on metabolism, food intake, medications, liver function, and many other factors. When in doubt, do not drive. If you or someone you know is struggling with alcohol, contact SAMHSA's National Helpline: 1-800-662-4357.

Body Weight (lbs)

Gender

Number of Drinks

Drink Type

Each equals ~1 standard drink (14g of pure alcohol)

Hours Since First Drink

Estimated BAC

0.000%

Impairment Level

Estimated Time Until Sober (0.00%)

BAC Impairment Scale

0.000.030.060.080.150.30+

BAC Over Time

Understanding Blood Alcohol Content (BAC)

Blood Alcohol Content, or BAC, is a measure of the amount of alcohol present in your bloodstream, expressed as a percentage by weight. A BAC of 0.08 percent means there are 0.08 grams of alcohol per 100 milliliters of blood. This is the legal limit for driving in all 50 U.S. states for adults over 21. Even at levels below 0.08 percent, alcohol impairs reaction time, judgment, and coordination, which is why many safety experts recommend not driving after any amount of drinking.

This calculator uses the Widmark formula, the most widely referenced method for estimating BAC. The formula accounts for the amount of pure alcohol consumed (in grams), body weight, and a gender-based distribution ratio known as the Widmark r factor. Males typically have an r factor of 0.68 and females 0.55, reflecting differences in body water percentage. The body eliminates alcohol at approximately 0.015 percent BAC per hour, regardless of body size, so the formula subtracts this metabolic rate multiplied by the hours elapsed since the first drink.

It is crucial to understand that this calculator provides rough estimates only. Actual BAC depends on many factors the formula cannot capture, including metabolic rate, liver health, food in the stomach, hydration level, medications, tolerance, and individual genetic variation. Two people of the same weight and gender can have meaningfully different BAC levels after consuming identical amounts of alcohol. Never rely on any calculator, app, or personal assessment to decide whether you are safe to drive. The only guaranteed way to avoid alcohol-impaired driving is to not drink before driving at all.

Health Disclaimer: This calculator provides rough estimates for educational purposes only. It should NEVER be used to determine fitness to drive or operate machinery. Individual alcohol metabolism varies greatly. Always err on the side of caution. If you or someone you know struggles with alcohol use, contact SAMHSA's National Helpline at 1-800-662-4357.

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