Alcohol Blood Concentration Calculator
Blood Alcohol (BAC) Calculator works out Estimated BAC now and BAC if all of it were absorbed and none eliminated from What to work out, Number of drinks and Size of each drink. The default figures on this page give estimated BAC now of 0.0425 % (g/100 mL); change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
11 steps
- Total liquid = 2 x 500 ml = 1000 mL
- Pure ethanol = 1000 mL x 5% = 50 mL
- Mass of ethanol = 50 mL x 0.789 g/mL = 39.45 g
- US standard drinks = 39.45 g / 14 g = 2.818
- UK units = 50 mL / 10 mL = 5
- Widmark ratio r = 0.68 (male)
- Body weight = 80 kg
- BAC before elimination = 39.45 g / (10 x 0.68 x 80) = 0.07252%
- Alcohol eliminated in 2 h = 0.015 x 2 = 0.03%
- BAC now = 0.07252 - 0.03 = 0.04252%
- Time until BAC reaches zero = 0.04252 / 0.015 = 2.83 h
Its 4 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
5 sources
What the Blood Alcohol (BAC) Calculator calculates
Estimates blood alcohol concentration from drinks, body weight, sex and time elapsed using the Widmark equation, and the time needed to fall back below a legal limit.
How to use this Blood Alcohol (BAC) Calculator
Enter What to work out, Number of drinks, Size of each drink and Drink size unit. Estimated BAC now updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Estimated BAC now, BAC if all of it were absorbed and none eliminated and BAC in per mille.
The method follows NHTSA, Office of Program Development and Evaluation - Computing a BAC Estimate (the Widmark form BAC = A x 5.14 / (W x r) - 0.015 H, with r = 0.68 men and 0.55 women), Widmark EMP, Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung, Berlin 1932 - original derivation of the distribution ratio r, NIAAA - What Is A Standard Drink? (0.6 fl oz / 14 g of pure alcohol), NHS - Alcohol units (one UK unit = 10 mL of pure alcohol) and NHTSA - The ABCs of BAC: A Guide to Understanding Blood Alcohol Concentration and Alcohol Impairment.
Two 500 mL beers at 5%, 80 kg man, two hours in example
With What to work out: bac, Number of drinks: 2, Size of each drink: 500, Drink size unit: ml, the calculator returns Pure alcohol consumed: 39.45, UK alcohol units (10 mL each): 5, BAC if all of it were absorbed and none eliminated: 0.0725. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Estimated BAC now, BAC if all of it were absorbed and none eliminated and BAC in per mille. The inputs you can vary are What to work out, Number of drinks, Size of each drink, Drink size unit, Alcohol by volume and Units.
Understanding Estimated BAC now, BAC if all of it were absorbed and none eliminated and BAC in per mille
This is a population-average estimate, not a measurement. Real BAC varies widely with absorption, food, sex, medication, liver function and tolerance, and can still be rising after the last drink. Never use it to decide whether it is safe or legal to drive. The only safe amount of alcohol before driving is none.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How do I calculate my blood alcohol?
Estimates blood alcohol concentration from drinks, body weight, sex and time elapsed using the Widmark equation, and the time needed to fall back below a legal limit. Open “How this is worked out” beside the result to see each step for your own figures.
How many drinks is .17 BAC?
On the figures this page opens with — number of drinks 2, size of each drink 500, alcohol by volume 5% and weight 80 — the estimated BAC now is 0.0425% (g/100 mL). No single number fits everyone: change any figure above and the answer updates as you type, with each step of the arithmetic beside it.
How many drinks is 0.08 BAC?
It needs What to work out, Number of drinks, Size of each drink, Drink size unit, Alcohol by volume and Units. Nothing else is required, and the figures stay in your browser.
What information do I need for the Blood Alcohol (BAC) Calculator?
You need What to work out, Number of drinks, Size of each drink, Drink size unit, Alcohol by volume, Units, Weight and Extra pounds. The page opens with default figures that give estimated BAC now of 0.0425 % (g/100 mL), so you can see the scale before entering your own.
What does this Blood Alcohol (BAC) Calculator show?
It shows Estimated BAC now, BAC if all of it were absorbed and none eliminated, BAC in per mille, Pure alcohol consumed, US standard drinks (14 g each), UK alcohol units (10 mL each), Hours until below the legal limit and Hours until no alcohol remains, with the working and any warnings for your entries.
Can I check how the Blood Alcohol (BAC) Calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.