Blood Alcohol (BAC) Calculator
Estimate blood alcohol concentration (BAC) from your drinks, body weight and time, with the Widmark formula.
About the Blood Alcohol (BAC) Calculator
The Widmark formula estimates BAC from grams of alcohol, body weight and how much of the body's mass holds alcohol (about 0.68 for men and 0.55 for women), then subtracts about 0.015% per hour as the liver clears it.
One US standard drink has 14 g of alcohol: 355 mL (12 oz) of 5% beer, 148 mL (5 oz) of 12% wine or 44 mL (1.5 oz) of 40% spirits.
The formula
BAC% = alcohol (g) ÷ (body weight (g) × r) × 100 − 0.015 × hours
- r
- 0.68 men, 0.55 women
- 0.015
- average elimination per hour
Worked example
Example: Estimated BAC = 0.046%
- Inputs: Units: lb / ft; Sex: Male; Weight: 180 lb; Standard drinks: 3; Hours since the first drink: 2 h.
- Formula: BAC% = alcohol (g) ÷ (body weight (g) × r) × 100 − 0.015 × hours
- Result: Estimated BAC = 0.046%
- Alcohol consumed: 42 g
- Hours until about 0.00%: 3
Things to keep in mind
- Never use this to decide whether it's safe to drive. Food, medicines, health and drink sizes change BAC a lot. If you drink, don't drive.
Questions people ask
Does coffee sober you up?
No. Only time lowers BAC.
What is the legal limit?
0.08% in the US, Canada and England and Wales; 0.05% in Scotland, most of Europe and Australia; lower or zero for new and commercial drivers in many places.