Important first
This calculator gives an estimate based on an average formula. How fast alcohol enters your blood and is broken down varies greatly between people and situations: whether you have eaten, how quickly you drank, your body composition, medication, tiredness and your health all play a part. Your actual BAC may therefore be considerably higher than the calculator shows. The only safe advice for driving is: if you drink, don't drive.
How the calculation works
The calculator uses the Widmark formula, used since the 1930s to estimate blood alcohol:
BAC (‰) ≈ grams of alcohol / (r × body weight in kg) − 0.15 × hours
Dividing per mille (‰) by 10 gives BAC as a percentage, the way it is usually expressed in the US and UK.
- Grams of alcohol: a US standard drink contains about 14 grams of alcohol: 12 oz of 5% beer, 5 oz of 12% wine or 1.5 oz of 40% spirits. Craft beers, large glasses of wine and generous home pours often contain much more, so count accordingly.
- r (distribution factor): the share of your body in which alcohol spreads, mostly water. The calculator uses 0.68 for men and 0.55 for women. Women have less body water on average and reach a higher BAC from the same amount.
- Elimination: the liver breaks down roughly 0.015% BAC per hour on average, varying from about 0.010 to 0.020. Coffee, cold showers and fresh air do not speed this up.
Worked example
A man weighing 180 lb (82 kg) has 4 standard drinks (56 grams of alcohol). Right after drinking his BAC would be about 56 / (0.68 × 82) ≈ 1.0 ‰, or 0.10%. After 2 hours, 0.03% has been broken down, leaving roughly 0.07%, and it takes nearly another five hours to reach zero.
A woman weighing 130 lb (59 kg) who has 3 drinks in one hour reaches about 0.11% according to the formula, well above the usual limit.
Common legal limits
- United States: 0.08% for most adult drivers in every state except Utah, where it is 0.05%. Commercial drivers are held to 0.04%, and drivers under 21 face zero-tolerance limits.
- England, Wales and Northern Ireland: 0.08% (80 mg per 100 ml of blood). Scotland: 0.05%.
- Most of continental Europe: 0.05%, often lower for new and professional drivers.
Even below the limit, your reaction time and judgement are affected. Always check the current rules where you are.
Why you may be over the limit anyway
- On an empty stomach alcohol is absorbed faster and the peak is higher.
- Drinking quickly produces a higher peak than the same amount spread over time.
- The morning after: after a heavy night you can still be over the limit the next morning.
- Medication and fatigue amplify the effects of alcohol.
Help and information
If you are worried about your own drinking or someone else's, talk to your doctor or contact a national helpline, such as SAMHSA's helpline in the US or Drinkline in the UK. To see how many calories drinks add to your day, use the calorie calculator.
Frequently asked questions
What is my BAC after one drink?
Roughly 0.02% to 0.04%, depending on your weight, sex and whether you have eaten.
How long does it take to sober up?
On average a little over an hour per standard drink, but it varies. The calculator gives an estimate.
Does coffee help you sober up?
No. Only time helps: the liver breaks down alcohol at a fairly fixed rate.
What is the legal limit?
0.08% in most US states and in England and Wales; 0.05% in Utah, Scotland and much of Europe.
Why do women reach a higher BAC?
Women have less body water on average, so the same amount of alcohol is dissolved in less fluid.
Can I use this to decide whether I can drive?
No. It is a rough estimate and your real BAC may be higher. Don't drive after drinking.
Last reviewed: 2026-10-06. Results are estimates for information only.