If liquor is marked "80 proof", what percent is the alcohol content?

When a liquor is marked "80 proof," it indicates that the alcohol content is 80 proof, which translates to 40% alcohol by volume (ABV). The proof system is a way of expressing the strength of alcoholic beverages, with the proof value being twice the percentage of alcohol. Therefore, to find the alcohol content in percentage, you simply divide the proof by two. In this case, 80 proof divided by 2 equals 40%. This measurement is a standard convention used in the United States, making the answer clear when understanding how proof corresponds to alcohol percentage.