Health

BAC Calculator

Estimate your blood alcohol concentration using the Widmark formula based on standard drinks consumed, body weight, biological sex, and hours elapsed since drinking.

Biological Sex

Weight Unit

Enter drinks and weight to see the result.

This calculator provides an estimate only. Actual BAC depends on many individual factors. Never drive after consuming alcohol.

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Widmark BAC Formula

The Widmark formula estimates BAC from the total alcohol consumed, body weight, body water distribution by sex, and the body's natural metabolism rate.

BAC = (alcohol_g ÷ (weight_kg × body_water)) × 100 − (0.015 × hours)

body_water: 0.68 (male) · 0.55 (female) · 1 standard drink ≈ 14g alcohol

This is an estimate only. Never drive after consuming alcohol regardless of calculated BAC.

Understanding BAC Levels

Blood alcohol concentration is measured as a percentage by weight of alcohol per unit of blood. At 0.02 to 0.04 percent, most people feel mild relaxation. At 0.05 to 0.07 percent, judgement and coordination begin to be affected. At 0.08 percent — the US legal driving limit — reaction time and multi-tasking ability are meaningfully impaired even if you feel fine.

The body metabolises alcohol at a roughly constant rate of about 0.015 percent BAC per hour regardless of coffee, food, or sleep. The only reliable way to become sober is to wait. A person at 0.12 percent needs approximately eight hours before reaching zero.

Use this tool for educational awareness only. Individual variation in alcohol metabolism is substantial, and no formula can reliably predict your exact BAC. Always err on the side of not driving if you have been drinking.

Frequently asked questions

How is blood alcohol concentration calculated?
Blood alcohol concentration is estimated using the Widmark formula. The formula divides the total grams of alcohol consumed by the person's body weight in kilograms multiplied by a body water constant of 0.68 for males and 0.55 for females. The result is then reduced by 0.015 percent per hour to account for the body's natural alcohol metabolism rate.
What counts as one standard drink?
In the United States, one standard drink contains approximately 14 grams of pure alcohol. This is equivalent to a 12-ounce regular beer at 5 percent ABV, a 5-ounce glass of wine at 12 percent ABV, or a 1.5-ounce shot of spirits at 40 percent ABV. Cocktails and craft beers often contain more than one standard drink due to higher ABV or larger serving sizes.
What is the legal driving limit in the United States?
The legal limit for driving in all 50 US states is a BAC of 0.08 percent. At this level, significant cognitive impairment, reduced reaction time, and diminished coordination are present. Many countries have lower limits of 0.05 percent. For commercial drivers in the US the limit is 0.04 percent, and for drivers under 21 it is effectively 0.00 percent in most states.
How accurate is the BAC estimate from this calculator?
This calculator provides an approximation only. Actual BAC varies significantly based on individual factors including rate of drinking, food consumption, medications, liver function, hydration level, and individual metabolism. The Widmark formula is a widely used scientific estimate but should never be relied upon to determine whether it is safe to drive. When in doubt, do not drive.
Why does biological sex affect BAC?
Biological sex affects BAC because males and females have different average proportions of body water, which is the medium in which alcohol distributes. Males typically have about 68 percent body water and females about 55 percent. Since alcohol is water-soluble, the same amount of alcohol distributes through a smaller volume of water in females, resulting in a higher BAC at the same body weight and drink count.
Does drinking coffee or food lower your BAC?
Food slows the absorption of alcohol into the bloodstream, which reduces the peak BAC you reach and spreads out the timeline of alcohol processing, but it does not eliminate alcohol or meaningfully lower BAC once alcohol is already in your system. Coffee and other caffeinated drinks do not lower BAC at all. Only time allows the liver to metabolise alcohol at its fixed rate of roughly 0.015 percent per hour.

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