BAC Calculator
Estimate blood alcohol content from your drinks, weight, sex and time with the Widmark formula, standard drinks by country and time to fall below 0.08 or 0.05.
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About this toolWhat is the BAC Calculator?
The BAC Calculator gives a rough estimate of blood alcohol concentration from what you drank, your body weight, your sex and the hours since your first drink. Enter how many beers, glasses of wine, spirits and other drinks you had; sizes and strengths are editable because a craft IPA at 7% in a 473 mL can is not the same as a 355 mL light beer. The page converts everything to grams of pure alcohol and applies the Widmark formula.
It shows the estimated BAC now, the higher figure if all the alcohol were absorbed at once, how many standard drinks you had under the US, UK, Canadian, Australian, New Zealand, Irish or WHO definition, and roughly how long until your level falls below 0.08%, 0.05% and 0.02% and close to zero.
Please treat the number as education, not permission. Individual BAC can be far higher than a formula predicts, and driving skills are affected well below any legal limit. Do not use this page to decide whether to drive.
- Widmark formula with the original 0.68 and 0.55 body water factors
- Editable sizes and ABV for beer, wine, spirits and other drinks
- Standard drinks for the US, UK, Canada, Australia, New Zealand, Ireland and WHO
- Time to fall below 0.08%, 0.05%, 0.02% and zero
- Shown in %, g/L and mg/100 mL, with the working
How to use the BAC Calculator
- Choose your sex and weight unit, then enter your body weight.
- Enter the hours since your first drink.
- Fill in how many beers, wines, spirits and other drinks you had, changing the size or ABV to match what you actually drank.
- Pick the standard drink definition for your country to see how many drinks or units that was.
- Read the estimated BAC, the time to fall below each reference level, and the worked formula. Then make plans that do not depend on the number.
Worked examples
Three beers and a glass of wine
Input
Male, 80 kg, 3 × 355 mL at 5%, 1 × 150 mL at 12%, 2 hours
Output
56.2 g alcohol (4.0 US standard drinks); estimated BAC 0.073%; about 4 h 53 min to zero
Peak 56.2 / (80,000 × 0.68) × 100 = 0.103%, minus 0.015 × 2 = 0.073%. Under 0.08% on paper, yet above the 0.05% limit in most of Europe and Australia, and someone with slower elimination could still be over 0.08%.
Two large glasses of wine
Input
Female, 60 kg, 2 × 150 mL at 13%, 1 hour
Output
30.8 g alcohol; estimated BAC 0.078%; about 1 h 53 min to fall below 0.05%
The same two glasses for an 80 kg man would give about 0.042% after an hour. Body water, not just weight, drives the difference.
Four pints in the UK
Input
Male, 85 kg, 4 × 568 mL at 4.5%, 3 hours, UK units
Output
80.7 g alcohol (10.1 UK units); estimated BAC 0.095%; about 6 h 18 min to zero
Even three hours after starting, the estimate is above the 0.08% England and Wales limit and nearly double Scotland's 0.05%. The morning after a late session is when many drink-driving arrests happen.
Background and insight
Erik Widmark, a Swedish chemist, published the equation in 1932: concentration = alcohol dose / (body weight × r), minus an elimination rate multiplied by time. The factor r is the share of body mass that alcohol dissolves into, essentially body water. Widmark measured averages of 0.68 for men and 0.55 for women; women typically have more body fat and less water per kilogram, so the same drinks produce a higher concentration. Forensic toxicologists still use the formula, but always with a range for r and for elimination, because both vary from person to person.
Grams of alcohol are volume × ABV × 0.789, the density of ethanol. A US standard drink is 14 g (0.6 fl oz of pure alcohol), equal to 12 fl oz of 5% beer, 5 fl oz of 12% wine or 1.5 fl oz of 40% spirits. A UK unit is 10 mL or 8 g. Canada defines a standard drink as 17.05 mL (13.45 g), and Australia, New Zealand and Ireland use 10 g. The same pint (568 mL) of 4.5% lager holds about 20 g of alcohol: 2.5 UK units, 1.4 US standard drinks or 2.0 Australian standard drinks.
The liver clears alcohol at a fairly constant rate, typically 0.010 to 0.020% per hour; this page uses 0.015%. Nothing speeds it up. Food in the stomach slows absorption, so the peak arrives later and lower, but it does not remove alcohol. BAC here is shown as a percentage (grams per 100 mL); 0.08% equals 0.8 g/L or 80 mg/100 mL, the units used in UK law.
Common use cases
Understanding standard drinks
See how a large glass of wine or a strong craft beer counts in your country's units.
Planning the morning after
Get a sense of how long alcohol may still be in your system before an early start.
Health and education
Show students or patients how weight, sex and drink size change blood alcohol.
Comparing drinking guidelines
Translate the UK 14 units a week or US two-drink daily guidance into the drinks you actually pour.
Tips and limitations
- The estimate can be off by 30% or more. Medication, illness, liver function, genetics and an empty stomach all push real BAC higher.
- Home pours are often larger than standard: a typical restaurant wine glass is 175 to 250 mL, not 150 mL.
- Check the ABV on the label. Many craft beers are 6 to 9%, so one can may be nearly two standard drinks.
- Sleep does not reset BAC. Six hours of sleep removes only about 0.09%, so a heavy night can leave you over the limit the next morning.
- Signs of alcohol poisoning include confusion, vomiting, slow or irregular breathing, and being hard to wake. Call emergency services and do not leave the person alone.
Frequently asked questions
How accurate are BAC calculators?
They give a population average. Real BAC for an individual can differ by a third or more because body water, absorption speed and liver elimination vary. A breathalyser or blood test is the only way to know, and even then impairment starts below legal limits.
How long does it take for alcohol to leave your system?
Blood alcohol typically falls by about 0.015% per hour, roughly one US standard drink per hour for an average adult. A BAC of 0.10% takes around six to seven hours to reach zero. Coffee, water, showers and exercise do not change this.
How many drinks to reach 0.08?
For an average 80 kg man, about four US standard drinks in an hour; for a 60 kg woman, about two to three. That is exactly why counting drinks is not a safe rule: size, strength, food and individual differences change the answer.
What is the Widmark formula?
BAC = alcohol in grams / (body weight in grams × r) × 100 − elimination rate × hours. Widmark's r is 0.68 for men and 0.55 for women, and a typical elimination rate is 0.015% per hour.
How many grams of alcohol are in a standard drink?
It depends on the country: 14 g in the US, 13.45 g in Canada, 10 g in Australia, New Zealand and Ireland, and 8 g in a UK unit. The WHO uses 10 g as a reference. Change the definition in the calculator to see your count in each.
Why do women reach a higher BAC from the same drinks?
On average women have a lower share of body water, so alcohol is less diluted, which Widmark captured with r = 0.55 against 0.68 for men. Differences in stomach enzyme activity may also play a smaller part.
Can I use this to know if I am safe to drive?
No. The estimate cannot account for your individual metabolism, and reaction time and judgement are affected from the first drink. If you have been drinking, use a taxi, public transport, a sober driver or stay where you are.
Is there an in-depth guide to the BAC Calculator?
Yes. “How Blood Alcohol Is Estimated: Widmark, Standard Drinks and Time” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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