Blood Alcohol Content (BAC) Calculator
Calculate your blood alcohol content (BAC) using the Widmark formula.
Know your impairment level, legal status, and time until sober before driving.
The Widmark Formula The Widmark formula, developed by Swedish physician Erik Widmark in the 1920s, is the gold standard for estimating blood alcohol content. It accounts for body weight, gender, alcohol consumed, and time elapsed.
Formula: BAC = (A × 5.14) / (W × r) − (0.015 × H)
Where:
- A = ounces of pure alcohol consumed
- W = body weight in pounds
- r = Widmark factor (0.73 for males, 0.66 for females)
- H = hours since drinking began
- 5.14 = conversion constant (converts oz alcohol to g, adjusts for blood volume)
- 0.015 = average alcohol metabolism rate (BAC% per hour)
Gender Difference The Widmark factor (r) differs by gender because females generally have a higher proportion of body fat and lower total body water, which means alcohol becomes more concentrated in their blood at the same dose.
Standard Drinks A standard drink in the United States contains 14 grams (0.6 oz) of pure alcohol. Common examples:
- Beer (5% ABV): 12 oz can/bottle
- Wine (12% ABV): 5 oz glass
- Spirits (40% ABV): 1.5 oz shot
Important Limitations This formula provides an estimate only. Actual BAC varies with food intake, individual metabolism, medications, liver health, and drinking speed. Never rely solely on this calculator to decide whether to drive.
Metabolism Rate The body metabolizes alcohol at roughly 0.015% BAC per hour — equivalent to about one standard drink per hour. This rate does not speed up with coffee, food, or exercise after drinking has begun.