BAC Calculator: Blood Alcohol Content Estimate
Estimate blood alcohol content with the Widmark formula from body weight, sex, drinks and time since drinking. Shows peak and current BAC in % and ‰ and the time to 0.08%, 0.05% and zero. It cannot tell you that you are safe to drive.
12 US fl oz (355 ml) at 5% ABV, about 14 g of alcohol
Enter your body weight to estimate your BAC.
About the BAC Calculator
The BAC Calculator estimates your blood alcohol content (BAC) from your body weight, your sex, the drinks you have had and the time since you started drinking. It shows the peak BAC, the BAC now, the total grams of alcohol, and how long it should take to fall under 0.08%, under 0.05% and back to 0.00%. Every figure is given as a percentage (grams per decilitre, the US convention) and in permille (grams per litre, the convention in much of Europe).
This calculator cannot tell you that you are safe to drive. The only safe BAC for driving is zero. Real blood alcohol depends on food, medicines, liver health, hydration and how quickly you drank, and two people with the same inputs can differ a great deal. Many countries set legal limits of 0.05% or lower, and some set zero for new or professional drivers. If you have been drinking, do not drive: take a taxi, public transport or a lift with a sober driver.
This is an estimate, not medical advice. If you or someone you know is worried about drinking, a doctor or a local alcohol support service can help. If someone is very drunk, cannot be woken, or is breathing slowly, call emergency services.
How to estimate your BAC
Steps
- Choose Male or Female and enter your body weight in kilograms or pounds.
- Enter the hours since your first drink.
- For each drink, pick a standard beer, wine or spirits measure and enter how many you had. Choose Custom drink to type any volume, in millilitres or US fluid ounces, and its strength as a percentage (ABV).
- Read the current BAC and the times until each threshold.
Standard drinks
The presets follow the US definition of a standard drink, about 14 grams of alcohol: 12 fl oz (355 ml) of beer at 5%, 5 fl oz (148 ml) of wine at 12%, and 1.5 fl oz (44 ml) of spirits at 40%. Drinks served in bars and at home are often larger or stronger, so use a custom drink when you know the real size.
The Widmark formula
The calculator uses the formula published by the Swedish chemist Erik Widmark in 1932, still the basis of most BAC estimates:
The distribution factor r is 0.68 for men and 0.55 for women, reflecting the share of the body that holds water. The elimination rate β is 0.015% per hour, a typical average; real rates range from about 0.010% to 0.025% per hour. The grams of alcohol in a drink are its volume in millilitres times its ABV times 0.789, the density of ethanol. Permille is the percentage times 10.
The formula assumes all the alcohol is absorbed at once, so the peak is the highest the estimate can be. In reality absorption takes 30 to 90 minutes, longer after a meal.
Worked example
A man weighing 80 kg drinks three standard beers. That is 3 × 355 ml × 0.05 × 0.789 = 42 g of alcohol. His peak estimate is 42 ÷ (80,000 × 0.68) × 100 = 0.077%, or 0.77‰. Two hours later it is 0.077 − 0.015 × 2 = 0.047%, and it should reach zero about 3 hours 9 minutes after that. He is still not safe to drive: impairment starts well below any legal limit.
Privacy
Everything is calculated in your browser. Nothing is uploaded, and your weight and drinks are never sent anywhere or saved.
Related tools
Convert between pounds and kilograms with the Mass Converter, and between millilitres and fluid ounces with the Volume Converter. The BMI Calculator relates your weight to your height.
Sources
- Widmark, E. M. P. (1932). Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung. Urban & Schwarzenberg, Berlin.
- National Institute on Alcohol Abuse and Alcoholism, What Is a Standard Drink?
- Jones, A. W. (2010). Evidence-based survey of the elimination rates of ethanol from blood with applications in forensic casework. Forensic Science International, 200(1–3), 1–20.
Open-source credits
The calculations are implemented in-house in TypeScript, with no third-party libraries. They follow the published Widmark formula with Widmark's distribution factors and an average elimination rate of 0.015% per hour, and the NIAAA definition of a standard drink.
Frequently asked questions
Can this calculator tell me if I am safe to drive?
No. It gives an estimate from average figures, and your real blood alcohol can be higher. Impairment begins well below the legal limit, and some countries set the limit at zero for new or professional drivers. The only safe BAC for driving is zero, so if you have been drinking, do not drive.
What is the difference between % and ‰?
Both measure the same thing. The percentage is grams of alcohol per 100 millilitres of blood (g/dL), used in the United States and the UK. Permille is grams per litre (g/L), used in much of Europe. To convert, multiply the percentage by 10: 0.05% is 0.5‰.
Why does the result differ for men and women?
Widmark's formula spreads the alcohol through the body's water. Women on average have a smaller share of body water than men of the same weight, so the same drink gives a higher concentration. The formula uses a factor of 0.68 for men and 0.55 for women.
Can I sober up faster with coffee, water or a cold shower?
No. The liver removes alcohol at a fairly steady rate, about 0.015% per hour on average, and nothing you drink or do speeds that up much. Coffee may make you feel more awake, but your BAC and your impairment stay the same.
How much alcohol is in a standard drink?
In the United States a standard drink holds about 14 grams of pure alcohol: 12 fl oz of beer at 5%, 5 fl oz of wine at 12% or 1.5 fl oz of spirits at 40%. Other countries define it differently; a UK unit, for example, is 8 grams. Use a custom drink to enter the real size and strength.