Vodka is made by distilling fermented agricultural products such as grains, potatoes, fruit or sugar. An alcohol’s strength is based on the amount of pure alcohol in the liquid. Distillers dilute the alcohol from the fermented product with water or other liquids. The alcohol in vodka can range in strength from a minimum of 30 percent of the total volume to 95 percent in grain alcohol.

A liquor’s proof is calculated by doubling the percentage of alcohol in the liquid. So, vodka that contains 30 percent alcohol would be 60 proof. Most vodka is 40 percent alcohol, or 80 proof. Vodka containing 60 percent of the total volume in alcohol is 120 proof.

The strength -- or percentage of alcohol -- in the drink determines how much alcohol reaches the blood stream. Alcohol is quickly absorbed into the bloodstream by the stomach and small intestine. Blood alcohol concentrations are measured by breath and/or urine tests. The BAC test registers about one-tenth of the concentration in the blood. A 150-pound person consuming 2 ounces of 80 proof alcohol would have a BAC of .037 percent after about 10 minutes. The same person consuming the same amount of 120 proof vodka would have a BAC of .057 percent. In most states, a BAC of .08 percent is considered legally drunk.

In addition to the percentage of alcohol, factors affecting the level of alcohol in the blood after one drink include sex, weight, ethnicity, tolerance and the amount of food in the stomach. A white male weighing 250 pounds who just ate dinner and has been drinking regularly for 25 years will not feel the effects of 120 proof vodka as quickly as a a 110 pound Asian female who ate six hours ago and is celebrating her 21st birthday with a shot of the same alcohol.