If a bottle of whiskey is labeled as 80 proof, what percentage of alcohol does it contain?

A whiskey labeled as 80 proof indicates that it contains 40% alcohol by volume. The proof system is a measure of the strength of alcoholic beverages, where the proof value is double the percentage of alcohol in the beverage. Therefore, to determine the alcohol content in percentage, you can take the proof value and divide it by two. In this case, 80 proof means it has 80 ÷ 2 = 40%. This standard is widely used in the United States for spirits, making it easy to understand the alcohol concentration in terms of proof.