Blood alcohol (BAC) calculator, Widmark formula
This tool estimates blood alcohol concentration after drinking, then subtracts what the body clears over time.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter sex, body weight, volume per drink, alcohol by volume (abv), number of drinks and hours since the first drink.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Alcohol grams = drinks × volume (mL) × ABV ÷ 100 × 0.789. Then BAC% = alcohol grams ÷ (body weight in grams × r) × 100 - β × hours, where r = 0.68 for men and 0.55 for women, and β is the elimination rate (0.015 per hour by default).
Example
Inputs: Sex = Male, Body weight = 70 kg, Volume per drink = 330 mL, Alcohol by volume (ABV) = 5 %, Number of drinks = 2. Result: Estimated BAC: 0.04 %; Per mille: 0.4 ‰; Pure alcohol consumed: 26 g.
Limits and caveats
- The r and β factors are averages that vary between people, so your real level can be clearly higher or lower.
- Do not rely on the result to decide whether to drive; the safe choice is not to drive after drinking.
- An educational estimate that does not replace assessment by a doctor or pharmacist.
Questions about this tool
What does a BAC of 0.05% mean?
About 0.05 g of alcohol per 100 mL of blood, which is 0.5 per mille.
Why does the result differ between men and women?
Women usually have less body water, so the same alcohol spreads into a smaller volume and the concentration is higher. The formula reflects this through the r factor.
Does coffee or water clear alcohol faster?
No. The liver removes alcohol at a roughly steady rate, and only time lowers the level.