How to use it
- Choose metric or US units and enter your body weight and sex.
- Enter how many standard drinks you had and pick the size of a drink that matches your country or label.
- Enter the hours since you started drinking. Read the estimated BAC now, the peak, and the hours until it would reach zero.
Warning. This is an estimate for general interest. It does not know what you ate, what you drank, your medicines or your health, and it can be wrong by a wide margin in either direction. Do not use it to decide whether to drive, ride, swim, operate machinery or take care of children. If you have been drinking, do not drive.
The formula
The calculator uses the formula of Erik Widmark (1932):
BAC (%) = alcohol in grams ÷ (r × body weight in grams) × 100 − 0.015 × hours
- alcohol in grams = number of drinks × grams of alcohol per drink (14, 10 or 8 g);
- r is the distribution factor: 0.68 for men, 0.55 for women (classic values);
- 0.015 % per hour is a typical elimination rate; individual rates range from roughly 0.010 to 0.020 % per hour;
- the result is never shown below zero, and the hours until zero are the BAC now divided by 0.015.
The peak shown is the BAC if all the alcohol were absorbed at once and none eliminated, so it is higher than the real peak of someone who drank over several hours.
Worked example
A man weighing 80 kg drinks three US standard drinks (3 × 14 g = 42 g) and it is two hours since the first one. Peak = 42 ÷ (0.68 × 80 000) × 100 = 0.0772 %. After two hours of elimination: 0.0772 − 2 × 0.015 = 0.0472 %, and he reaches zero after about 3.1 hours.
Limits of the estimate
- Food in the stomach slows absorption; fizzy or warm drinks speed it up. The formula assumes none of this.
- Body fat, age, medicines, liver health and tolerance change real values.
- Legal limits differ – for example 0.08 % in most US states and 0.05 % in many other countries, with lower or zero limits for some drivers. Being under a limit does not mean you are unimpaired.
- This is general information, not medical advice. If you are worried about your drinking, talk to a doctor.