The calculator uses the Widmark formula: BAC (%) = alcohol in grams / (body weight in kg x r x 10) minus 0.015 per hour. Alcohol grams = standard drinks x 14 (the US standard drink). The Widmark factor r is 0.68 for men and 0.55 for women, reflecting average body water. The body clears roughly 0.015% BAC per hour (range about 0.010-0.020). The result is a rough estimate: food, drink strength, medication, health, genetics and how fast you drank all change the real value. Only a breathalyser or blood test measures BAC. Never use an estimate to decide whether it is safe to drive: if you have been drinking, do not drive.
| Body weight | Man, 2 drinks | Man, 4 drinks | Woman, 2 drinks | Woman, 4 drinks |
|---|---|---|---|---|
| 120 lb (54 kg) | 0.046 | 0.121 | 0.064 | 0.157 |
| 140 lb (64 kg) | 0.035 | 0.100 | 0.050 | 0.130 |
| 160 lb (73 kg) | 0.027 | 0.083 | 0.040 | 0.110 |
| 180 lb (82 kg) | 0.020 | 0.071 | 0.032 | 0.095 |
| 200 lb (91 kg) | 0.015 | 0.061 | 0.026 | 0.082 |
| 220 lb (100 kg) | 0.011 | 0.053 | 0.021 | 0.072 |
| 240 lb (109 kg) | 0.008 | 0.046 | 0.017 | 0.064 |
By the Widmark formula, about 3 standard drinks drunk quickly put a 170 lb (77 kg) man at 0.08, and about 2 put a 140 lb (64 kg) woman there; spreading them over a few hours lowers the peak by about 0.015 per hour. It varies a lot between people, so there is no number that is safe for everyone.
About 0.015 BAC per hour, so a BAC of 0.08 takes around 5 hours to reach zero. Coffee, cold showers or water do not speed this up.
0.08% in most of the United States (0.05% in Utah) and in England, Wales and Northern Ireland; 0.05% in Scotland, Australia and most of Europe; 0.02% or lower in several countries, and often zero for new or commercial drivers. Impairment starts well below the legal limit.
On average women have less body water and less of the enzyme that breaks down alcohol in the stomach, so the same amount of alcohol gives a higher concentration. The calculator reflects this with a lower Widmark factor.
For education only. This is an estimate and cannot tell you whether you are safe to drive, operate machinery or make decisions. If you are unsure, do not drive: use a taxi, a ride share or a sober friend. If you or someone else shows signs of alcohol poisoning (confusion, vomiting, slow breathing, unconsciousness), call emergency services.
See also: water intake calculator · calories burned calculator · BMI calculator · BMR and calorie calculator · TDEE calculator · all tools