BAC Calculator

Frequently Asked Questions

What is the legal BAC limit for driving in the US?

For non-commercial drivers age 21 and over, the legal limit is 0.08% in all 50 states. For commercial drivers it is 0.04%. For drivers under 21, most states enforce zero-tolerance laws at 0.00 to 0.02%. Many countries use a 0.05% limit.

How long does it take to sober up?

The liver clears alcohol at a rate of roughly 0.015% BAC per hour for most adults, equivalent to about one standard drink per hour. A person at 0.10% BAC will need approximately 6 to 7 hours to reach 0.00%. Only time works; there is no proven method to speed clearance.

Why does sex affect BAC?

Males typically have more body water relative to total body weight (about 73%) compared to females (about 66%). Since alcohol distributes into body water, females reach a higher BAC than males of the same weight drinking the same amount. Hormonal differences in gastric alcohol dehydrogenase activity also play a role.

Can I trust this calculator before deciding to drive?

No. This is an estimate based on population averages. Individual variation can be substantial. Even a BAC well below 0.08% impairs reaction time and divided attention. The only safe choice after consuming alcohol is not to drive. Always arrange a designated driver or rideshare.

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General information only. Not medical advice.

Health & Medical Disclaimer: General information only. Not medical advice.

This calculator provides general health information only and is not medical advice. Results do not replace professional medical evaluation or diagnosis. Consult a licensed healthcare provider before making health decisions. Always seek immediate medical attention for emergencies.

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How This Calculator Works

Enter your body weight (in lb or kg), biological sex, the number of drinks consumed, each drink's volume in fluid ounces, its ABV percentage, and the hours since you had your first drink. The tool converts the alcohol to grams, applies the Widmark formula to estimate your blood alcohol concentration (BAC), subtracts what your liver has metabolized over time, and reports an impairment status plus an estimate of hours until sober. Results are informational only and never substitute for direct blood alcohol measurement.

The Widmark Formula

The Widmark estimate is: BAC = (grams of alcohol ÷ (body weight in grams × r)) × 100 − 0.015 × hours, where r is the body-water distribution factor (0.73 for males, 0.66 for females). Alcohol grams are calculated as: fluid ounces × ABV% × 0.0296 × 789.24, which converts volume to mass using ethanol's density of approximately 0.789 g/mL. The 0.015 per hour term reflects the liver's average clearance rate of roughly one standard drink equivalent per hour. The sex-based r factor exists because males typically have proportionally more body water than females at the same weight, diluting alcohol further.

BAC Impairment Levels

Below 0.02%: No measurable impairment for most people, though reaction time may be slightly affected.

0.02 to 0.05%: Mild relaxation, slightly reduced inhibition, minor impairment in divided attention tasks.

0.05 to 0.08%: Noticeable impairment in coordination, judgment, and reaction time; driving is risky.

0.08 to 0.15%: Significant impairment; the legal limit in most US states is 0.08%. Nausea, loss of balance, slurred speech.

Above 0.15%: Severe impairment; vomiting, loss of consciousness risk increases significantly.

Above 0.30%: Life-threatening respiratory depression risk in non-tolerant individuals.

What Is a Standard Drink?

In the United States, one standard drink contains approximately 14 grams of pure alcohol. Common equivalents: 12 fluid ounces of regular beer at 5% ABV, 5 fluid ounces of wine at 12% ABV, or 1.5 fluid ounces of distilled spirits at 40% ABV. Craft beers, large wine pours, and cocktails often contain 1.5 to 3 standard drink equivalents. Entering the actual ABV and fluid ounces rather than simply counting drinks gives a more accurate estimate when beverages vary.

Factors That Affect Real BAC

The Widmark formula is a population average and will not match every individual precisely. Factors that lower real BAC relative to the estimate include recent food consumption (slows absorption), higher fitness level and muscle mass, and faster individual CYP2E1 enzyme activity. Factors that raise real BAC include drinking on an empty stomach (peak BAC 30-60 minutes vs. 1-2 hours with food), carbonated mixers (accelerate absorption), dehydration, liver disease, and certain medications. Tolerance affects perceived impairment but not BAC itself - a tolerant drinker feels less impaired at 0.10% but is equally impaired on objective tests.

Important Note

This calculator is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider before making any health-related decisions. Never drive or operate machinery after consuming alcohol, regardless of the estimated BAC. Only time eliminates alcohol; coffee, water, food, and exercise do not lower BAC. Legal limits vary by jurisdiction and by driver category (commercial, under 21, etc.).

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