Blood Alcohol Content (BAC) Calculator
Estimate blood alcohol concentration (educational only).
A rough Widmark estimate of blood alcohol — for education only, NOT for deciding whether to drive. Never drive after drinking.
How the Math Works
The Widmark formula calculates blood alcohol concentration (BAC) using three key variables: the grams of alcohol consumed, your body weight adjusted by a distribution ratio (r), and time. The formula BAC = alcohol(g) ÷ (weight·r) − 0.015·hours works by first determining how much alcohol disperses in your system based on your physical characteristics, then subtracting the natural metabolism that occurs at approximately 0.015% per hour. The distribution ratio (r) accounts for differences in body composition, typically ranging from 0.55 for women to 0.68 for men, reflecting how water and fat affect alcohol distribution in the body.
Practical Applications
To use this calculator practically, first determine the grams of alcohol by multiplying the volume consumed (in milliliters) by the alcohol by volume (ABV) percentage, then dividing by 100. For example, a standard 1.5-ounce (44ml) shot of 40% whiskey contains approximately 17.6 grams of pure alcohol. Input your weight in kilograms along with your gender to automatically apply the correct distribution ratio, then enter the hours since your first drink. The calculator will output your estimated BAC, which remains for informational purposes only and should never be used to determine driving safety.
Day-to-Day Use
This BAC calculator serves as an educational tool for understanding alcohol metabolism and personal responsibility. By tracking your estimated BAC, you can make informed decisions about drinking duration and pace, ensuring adequate time for alcohol processing before operating vehicles or engaging in activities requiring full cognitive function. The calculator also helps individuals develop realistic expectations about how their body processes alcohol, potentially preventing overestimation of one's sobriety level and promoting safer social drinking habits in everyday situations like dining out or attending events.
Worked example
3 drinks, 70 kg male, 2 h → ~0.058%.
FAQ
Is this legal proof?
No — it's a rough estimate. Many factors affect real BAC; never use it to judge fitness to drive.