BAC calculator
Blood alcohol level and sobering-up time
About you
Men and women hold a different share of body water, which changes the result.
Use height and age (Watson)
Works out your own distribution factor instead of the average for your sex.
What you drank
Tap to add a drink
No drinks added yet.
Another drink
Pure alcohol: 0 g= 0 standard drinks
Time since the first drink
Enter your body weight to see a result.
Estimate only, not a basis for deciding whether to drive. The only safe choice is not to drive after drinking. Disclaimer
Enter what you drank and how long ago. The result is an estimate of your blood alcohol content from the Widmark formula — never a green light to drive.
How to use the BAC calculator
- Pick man or woman and type your body weight. Switch to lb if you think in pounds.
- Tap the drinks you had. Tap the same one again for a second glass, or open Another drink for a size that is not listed.
- Say how long ago the first drink was, in hours and minutes or as clock times.
- Choose the country whose limit you want to compare with. The reading, the time back to zero and the curve update as you type.
Method: BAC = A / (r × W) − β × t · r 0.68 / 0.55 · β 0.15 ‰/h · 0.08 % · Updated October 26, 2026
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CalculatorsBlood alcohol level and sobering-up time
Limits & drinksLegal limits by country and what one drink holds
Blood alcohol calculator: what the number means
Blood alcohol content is the mass of alcohol in a volume of blood. Europe writes it in per mille (‰), grams of alcohol per litre of blood. The United States writes the same quantity as a percentage (% BAC), grams per 100 millilitres. They differ only by a factor of ten: 0.8 ‰ is the same reading as 0.08 %.
This BAC level calculator shows both, because the figure you need depends on where you are. France states the limit in g/l, the United Kingdom in mg per 100 ml, Japan in mg per litre of breath. The legal limits page lists each country the way its own law words it.
The formula behind the result
The calculator uses the Widmark equation, published by Erik Widmark in 1932 and still the basis of forensic alcohol calculations:
BAC = A / (r × W) − β × t
A is the grams of pure alcohol you drank, W your body mass in kilograms, t the hours since the first drink. r is the Widmark factor, the share of your body that behaves like water towards alcohol: on average 0.68 for men and 0.55 for women. β is how fast you clear alcohol, taken here as 0.15 ‰ per hour.
Grams of alcohol come from the drink itself: millilitres × alcohol by volume × 0.789, because a millilitre of pure ethanol weighs 0.789 g at 20 °C. A 0.5 l beer at 5 % therefore holds about 19.7 g.
Switch on height and age and the factor is worked out for your body instead, from the Watson total-body-water equations. It is a better fit than a population average, but it is still a model of a body, not a measurement of yours.
Why this is an estimate and not a reading
Widmark describes an average adult with a steady liver. Real people are not averages. Elimination runs from roughly 0.10 to 0.20 ‰ per hour between individuals; food in the stomach delays absorption by an hour or more; medicines, illness, tiredness and how often you drink all move the figure. A heavy session can still be rising hours after the last glass.
A forensic laboratory measures blood. A police breath tester measures breath. Neither of those is what a page of arithmetic can give you. Use the number to understand the scale of what you drank, and nothing else.
The most accurate BAC calculator is still only a model
People search for the most accurate BAC calculator, so it is worth being plain: no calculator can be accurate about one person. What a good one can do is be honest about its inputs, use the drink sizes that are actually sold where you live, show you the working, and name the law it compares you with. That is what this one does, and the figures it prints come from the same tested module in every language.
Related guides
Frequently asked questions
How do you calculate BAC by hand?
Work out the grams of alcohol (millilitres × % vol × 0.789), divide by your weight in kg times 0.68 for a man or 0.55 for a woman, and subtract 0.15 for every hour since the first drink. The answer is in per mille; divide by ten for % BAC.
How many drinks make 0.08 %?
There is no answer that holds for two people. 0.08 % is 0.8 ‰, and a 70 kg man reaches it from roughly four US standard drinks with no time to clear them, while a 55 kg woman can pass it on two. That is exactly why the only safe level for driving is zero.
Is a BAC calculator legally valid?
No. Nothing on this page is evidence of anything. Courts and police act on measured blood or breath samples, not on an estimate from body weight.
Does coffee, food or a cold shower bring my BAC down?
No. Your liver clears alcohol at its own pace and nothing you eat, drink or do speeds it up. Coffee makes a drunk person an awake drunk person. Only time lowers the number.
Why do men and women get different results from the same drinks?
Alcohol spreads through body water, and on average women carry a smaller share of water for their mass. The same drink therefore reaches a higher concentration. The calculator uses 0.68 and 0.55 for that, or your own factor if you give height and age.
Every figure on this page is an estimate from an average body. Your own reading can be higher.