A variety of factors affect a drinker's BAC. The rate of alcohol consumption, the gender and size of the drinker, and how much food is in the stomach all affect BAC.
Rate of Consumption A person's liver chemically breaks down, or metabolizes, alcohol at a fairly constant rate. That rate is about one half to one ounce of alcohol per hour—the approximate amount of alcohol in one can of beer, one shot of liquor, or one glass of wine. Therefore, people who have a few drinks in one hour have a higher BAC than people who drink the same amount over several hours.
Gender At the same rate and amount of alcohol consumption, males generally will have a lower BAC than females. This is because, for males, a larger portion of the alcohol gets metabolized in the stomach before it enters the bloodstream. In addition, the liver is more efficient at metabolizing alcohol in males.
Body Size In general, smaller people—by weight and height—feel the effects of alcohol more than larger people. They will have a higher BAC after a similar number of drinks.
Amount of Food in the Stomach Drinking on an empty stomach increases the rate of alcohol absorption into the bloodstream. A higher BAC will result.