Blood Alcohol Calculator
Estimate blood alcohol concentration (BAC) from your weight, drinks and time, using the Widmark formula.
Reviewed October 7, 2026 Runs in your browser — inputs are never stored
This tool provides general educational estimates only and is not medical advice. It does not diagnose, treat, or replace guidance from a qualified healthcare provider. Consult a doctor for decisions about your health.
About the Blood Alcohol Calculator
The blood alcohol calculator estimates your blood alcohol concentration (BAC) with the Widmark formula. It divides the grams of alcohol consumed by your body weight multiplied by a distribution factor (0.68 for men, 0.55 for women), converts the result to a percentage and subtracts about 0.015% for every hour since you started drinking. The estimate is approximate: food, medication, hydration and individual metabolism can change real BAC considerably. Never use it to decide whether you are safe to drive. Legal limits vary by country, and in some countries the limit is zero.
How to use it
- 1Select your sex and enter your body weight.
- 2Enter the number of drinks and the grams of alcohol per drink (a U.S. standard drink is 14 g).
- 3Enter the hours since your first drink.
- 4Press Calculate to see your estimated BAC.
Worked example
a 75 kg man who has three standard drinks (42 g of alcohol) over two hours has an estimated BAC of 42 ÷ (75,000 × 0.68) × 100 − 0.015 × 2 ≈ 0.05%.
How it works
Widmark formula
BAC = (alcohol grams / (weight g × r)) × 100 − 0.015 × hours, where r is 0.68 (men) or 0.55 (women).
Who it is for
Adults who want to understand how alcohol builds up and clears from the body.
Why it helps
It shows how quickly a few drinks raise BAC and how slowly the body removes alcohol.
Common use cases
- Understanding how body weight and sex affect BAC
- Seeing how long alcohol takes to clear
- Learning how the Widmark formula works
Common mistakes to avoid
- Assuming a result below the legal limit means you are safe to drive.
- Using the number of glasses instead of grams of alcohol — drink sizes and strengths vary.
Frequently asked questions
A:No. Never rely on any BAC estimate to decide whether to drive — if you have been drinking, do not drive.
A:On average about 0.015% BAC per hour, but this varies between people.
Reviewed for accuracy · Last updated October 7, 2026
Formulas follow recognised clinical references — including WHO BMI classifications, the Mifflin-St Jeor equation, and Naegele’s rule — and are periodically checked against published reference values.
CalcWisee Editorial Team
Calculator development and formula review
CalcWisee is an independent site founded by Ayman. Every calculator is built from a published formula or official definition, tested against hand-worked examples before it goes live, and corrected promptly when a reader reports an issue to ayman@calcwisee.com.
Expertise: Financial mathematics, Health and fitness formulas, Applied mathematics, Unit conversion standards
References & sources
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