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BAC Calculator

Educational blood alcohol content (BAC) estimate using body weight, standard drinks, and time. Do not use to make driving or safety decisions.

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Formula

BAC estimate uses a Widmark-style approach: alcohol distributed by body water minus alcohol eliminated over time

Standard drinks are modeled as fixed alcohol grams. The estimate applies a gender-based body water constant and subtracts a typical elimination rate over time.

Worked Example

Male, 180 lbs, 3 standard drinks, 2 hours. The tool estimates BAC and includes a safety warning that calculator estimates are not reliable for driving decisions.

How Blood Alcohol Content is Estimated

This calculator uses the Widmark formula, a widely referenced method that estimates BAC based on the amount of alcohol consumed, body weight, gender, and time elapsed since drinking.
  • The Widmark formula distributes alcohol across body water volume, which differs between males (approximately 68%) and females (approximately 55%) by body weight
  • One standard drink contains approximately 14 grams of pure alcohol, equivalent to 12 oz beer at 5%, 5 oz wine at 12%, or 1.5 oz spirits at 40%
  • The body eliminates alcohol at an average rate of 0.015% BAC per hour, though individual rates can vary from 0.010% to 0.020%
  • Food in the stomach slows alcohol absorption but does not change the total amount absorbed, meaning it delays but does not reduce peak BAC

This calculator is for educational purposes only. Individual BAC varies significantly based on metabolism, food intake, hydration, medications, and other factors. Never use any BAC estimate to make driving or safety decisions.

Frequently Asked Questions

Is this estimate accurate enough to decide whether to drive?

No. BAC estimates vary widely based on individual biology, food intake, hydration, medications, and actual drink sizes. Never use any calculator to make driving decisions. Plan safe transportation in advance.

What counts as one standard drink?

In the US, one standard drink contains approximately 14 grams of pure alcohol. This equals 12 oz of regular beer (5% ABV), 5 oz of wine (12% ABV), or 1.5 oz of distilled spirits (40% ABV). Craft beers and cocktails often contain significantly more alcohol than one standard drink.

How long does it take for BAC to return to zero?

The body eliminates alcohol at an average rate of about 0.015% BAC per hour. A BAC of 0.08% would take roughly 5 to 6 hours to fully eliminate, though individual rates vary. Sleep, coffee, and cold showers do not speed up elimination.

Does eating food reduce BAC?

Eating before or while drinking slows alcohol absorption, which can lower peak BAC. However, food does not reduce the total amount of alcohol absorbed. The same total alcohol will eventually reach your bloodstream regardless of food intake.

What is the legal BAC limit for driving?

In most US states, the legal limit is 0.08% for drivers aged 21 and over. Many states have lower limits for commercial drivers (0.04%) and zero tolerance for drivers under 21. Legal limits vary by country and jurisdiction.

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