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What Is BAC?
Blood Alcohol Content (BAC) measures the concentration of alcohol in your bloodstream, expressed as a percentage. A BAC of 0.08% means there are 0.08 grams of alcohol per 100 milliliters of blood. This is the legal driving limit in most US states and many countries worldwide. BAC is affected by the number of drinks consumed, body weight, gender, the rate of consumption, and the time elapsed since drinking.
The Widmark Formula
This calculator uses the Widmark formula, the most widely accepted method for estimating BAC. The formula is: BAC = (A / (W x r)) x 100 - (0.015 x H), where A is the total alcohol consumed in grams, W is body weight in grams, r is the Widmark factor (0.68 for men, 0.55 for women), and H is hours since drinking began. The 0.015 constant represents the average rate at which the body metabolizes alcohol per hour.
Standard Drink Equivalents
One standard drink contains approximately 14 grams (0.6 ounces) of pure alcohol. This is roughly equivalent to 12 oz of regular beer (5% ABV), 5 oz of wine (12% ABV), or 1.5 oz of distilled spirits (40% ABV). Many cocktails contain multiple standard drinks. Understanding standard drink sizes is essential for accurately estimating your BAC.
Impairment by BAC Level
At 0.02% BAC, slight mood changes and relaxed inhibitions occur. At 0.05%, judgment and coordination decline. At 0.08%, muscle coordination is significantly impaired, reaction time increases, and judgment is poor. At 0.10%, reaction time and control deteriorate further. Above 0.15%, major loss of balance and substantial impairment occurs. At 0.30% and above, there is risk of unconsciousness and death.
Factors Affecting BAC
BAC varies based on several factors beyond the number of drinks. Women typically reach higher BAC levels than men of the same weight due to differences in body composition (higher fat-to-water ratio). Drinking on an empty stomach leads to faster absorption and higher peak BAC. Medications, liver health, and individual metabolic differences also play significant roles.