Free Blood Alcohol Content Calculator
Estimated blood alcohol content by the Widmark formula.
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Inputs
Result
Estimated BAC
5.235%
Impaired — do not drive
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Short answer
BAC (Widmark) = (alcohol grams × 100) ÷ (weight g × distribution ratio) − elimination × hours. The result is not medical advice — never drive after drinking.
What is the BAC Calculator?
Blood Alcohol Content is the mass ratio of alcohol to blood, typically expressed as a percent (0.08% is the US legal driving limit).
How does the BAC Calculator work?
Convert drinks to grams of alcohol (14 g per standard US drink). Divide by body water. Subtract elimination based on time since first drink.
Formula
Variables
ratioBody water distribution — 0.68 male, 0.55 female0.015Average elimination rate per hour
Explanation
Widmark's 1932 formula. Individual variability is significant — this is an estimate only.
Examples
Example 1: 75 kg male, 3 drinks, 2 hours
Estimated BAC ~0.052%, likely impaired.
Applications
- Rough personal awareness
- Never a substitute for a breathalyzer
Advantages
- Widely referenced formula
Limitations
- Ignores food, medications, genetics, drink strength variation
- Not medical or legal advice
Common mistakes
- Assuming beer, wine, and cocktails are all 'one drink'
Tips
- A standard drink = 12 oz beer @ 5% = 5 oz wine @ 12% = 1.5 oz spirits @ 40%
Related concepts
The BAC Calculator sits inside the Health Calculators hub, in the clinical & medical metrics cluster. Laboratory and screening ratios. Understanding the terms below makes the output easier to interpret and easier to compare against neighbouring measures.
Practical use cases and industry applications
Understanding BAC
Blood Alcohol Content is the mass ratio of alcohol to blood, typically expressed as a percent (0.08% is the US legal driving limit). Within health calculators, bac belongs to the clinical & medical metrics cluster, where it shares terminology and assumptions with closely related tools.
Learning how bac is calculated
Widmark's 1932 formula. Individual variability is significant — this is an estimate only. Working through the variables one at a time — ratio, 0.015 — makes the result reproducible by hand and easier to sanity-check.
Using bac to make a decision
Rough personal awareness Never a substitute for a breathalyzer Because outputs depend on the assumptions you enter, run more than one scenario before committing to a figure.
How bac compares with related measures
renal function, reference range, screening threshold, risk category all describe adjacent aspects of clinical & medical metrics. Comparing this calculator's output against those measures — using the related tools listed on this page — prevents a single metric from being read in isolation.
Frequently asked questions
How reliable is this?
Directional only. Actual BAC varies 20–30% between individuals with identical inputs. Never rely on a calculator to decide whether to drive.
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