About the Blood Alcohol (BAC) Calculator
This blood alcohol calculator estimates your blood alcohol concentration (BAC) using the Widmark formula — the classic method used in forensic toxicology. Enter how many standard drinks you have had, your body weight, your sex and how many hours have passed since your first drink, and it estimates your current BAC, your peak level and how long your body needs to clear the alcohol.
You can choose US, UK, Australian or Canadian standard drink sizes and compare the result against a 0.08%, 0.05% or 0.02% legal limit, since limits differ between countries, US states and driver categories. The chart shows how your estimated BAC falls hour by hour.
Treat the result as a rough educational estimate only. Real BAC varies with food, drinking speed, medication, liver health and genetics, and elimination can be slower than the 0.015% per hour average used here. Never use a calculator to decide whether you are safe to drive — if you have been drinking, do not drive.
With the default inputs, the estimated bac now is 0.056%. Change any value above to recalculate instantly.
How to use the blood alcohol (bac) calculator
- 1Select your sex and enter your body weight.
- 2Enter how many drinks you have had and pick your country’s standard drink size.
- 3Enter the hours since you started drinking.
- 4Choose the legal limit that applies to you.
- 5Read your estimated BAC and how long until it falls under the limit and to zero.
Formula and method
The Widmark formula spreads the grams of alcohol consumed (A) through the body water, approximated as body weight in grams (W) times a distribution factor r — about 0.68 for men and 0.55 for women, who on average have a higher proportion of body fat. That gives the peak BAC as if all the alcohol had been absorbed at once.
The liver then removes alcohol at a roughly constant rate, β, averaging about 0.015 percentage points per hour (the range is roughly 0.010–0.020). Subtracting β × hours since the first drink gives the current estimate. Because absorption actually takes 30–90 minutes, BAC shortly after drinking may still be rising, so early estimates can understate the true peak.
- A
- Grams of pure alcohol (drinks × grams per drink)
- W
- Body weight in grams
- r
- Widmark factor: 0.68 men, 0.55 women
- β
- Elimination rate, ≈ 0.015% per hour
- t
- Hours since the first drink
Worked examples
180 lb man, 4 US drinks over 3 hours
Four US drinks contain 56 g of alcohol. Spread through 81.6 kg × 0.68 of body water, the peak is about 0.101%. After 3 hours at 0.015% per hour the estimate is about 0.056% — under 0.08%, but it takes around 3.7 more hours to reach zero.
140 lb woman, 5 drinks over 2 hours
70 g of alcohol in a 63.5 kg woman with r = 0.55 gives a peak of about 0.200%. Two hours later she is still around 0.170%, more than twice the 0.08% limit, and needs about 6 more hours to fall below it.
Metric: 75 kg man, 3 Australian standard drinks, 1 hour, 0.05% limit
Three 10 g Australian standard drinks are 30 g of alcohol. 30 ÷ (75,000 × 0.68) × 100 ≈ 0.059% at peak, minus 0.015% after one hour leaves about 0.044%. Because absorption can take up to 90 minutes, the true level may still be rising.
Frequently asked questions
How long does it take to sober up?+
The liver clears alcohol at roughly 0.015% BAC per hour on average (typically 0.010–0.020%). For an average-sized man one US standard drink raises BAC by about 0.02–0.025%, so each drink takes well over an hour to clear. Nothing — coffee, water, food after drinking or a cold shower — meaningfully speeds this up; only time does.
What BAC is the legal limit for driving?+
It is 0.08% in all US states except Utah (0.05%), and 0.08% in England and Wales but 0.05% in Scotland. Most of Europe and Australia use 0.05%, and commercial drivers in the US are held to 0.04%. Many places have lower or zero limits for new drivers.
Why do women reach a higher BAC than men?+
On average women have a lower proportion of body water and a higher proportion of body fat at the same weight, so the same amount of alcohol is less diluted. The Widmark factor reflects this: about 0.55 for women versus 0.68 for men.
How accurate is a BAC calculator?+
It is only an approximation. Food in the stomach, drinking speed, medications, liver function and individual metabolism can shift real BAC well above or below the estimate. Only a calibrated breath or blood test measures BAC.
What counts as one standard drink?+
In the US a standard drink contains 14 g of pure alcohol: 12 oz of 5% beer, 5 oz of 12% wine or 1.5 oz of 40% (80-proof) spirits. A UK unit is 8 g, and an Australian standard drink is 10 g.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.