Estimate your Blood Alcohol Content (BAC) using the Widmark formula. Enter your weight, sex, drinks consumed, and time elapsed since drinking.
Euphoria. Mild impairment of judgment, memory, and attention.
| BAC Level | Effects |
|---|---|
| < 0.020% | Subtle effects |
| 0.020–0.050% | Mild impairment |
| 0.050–0.080% | Legal limit (US) |
| 0.080–0.100% | Significant impairment |
| 0.100–0.150% | Serious impairment |
| 0.150–0.300% | Severe impairment |
Our free BAC (Blood Alcohol Content) calculator estimates your approximate blood alcohol level based on the number and type of drinks you've had, your body weight, sex, and time elapsed since drinking, using the scientifically established Widmark formula. This tool is for educational purposes only and should never be used to decide whether it's safe to drive.
BAC (%) = [ Alcohol Consumed (grams) ÷ (Body Weight (grams) × r) ] × 100 − (Elimination Rate × Hours Elapsed)
Here, r is the Widmark distribution ratio, roughly 0.68 for men and 0.55 for women, reflecting differences in body water content. The elimination rate assumes the average body metabolizes alcohol at about 0.015% BAC per hour. Grams of alcohol per drink are calculated from the drink's volume, alcohol-by-volume (ABV) percentage, and ethanol's density.
This formula produces an estimate, not a precise measurement, actual BAC varies with metabolism, food intake, medications, and other individual factors that a formula cannot fully capture.
In all US states, the legal limit for driving is 0.08% BAC for drivers 21 and older, though impairment can begin well below this level. Commercial drivers face a stricter 0.04% limit, and most states have zero-tolerance policies for drivers under 21.
A BAC calculator provides an estimate based on averages, actual BAC can be affected by food intake, medications, liver function, hydration, and individual metabolism, so real BAC can differ meaningfully from the calculated estimate in either direction.
The body eliminates alcohol at roughly 0.015% BAC per hour on average, so it can take several hours for BAC to return to zero after a night of drinking, longer than most people expect. Coffee, cold showers, and food do not speed up alcohol elimination.
Women generally have a lower percentage of body water relative to body weight than men, which means the same amount of alcohol becomes more concentrated in a woman's bloodstream, resulting in a higher estimated BAC for the same weight and number of drinks.