What alcohol content does 100 proof represent in percentage?

100 proof represents an alcohol content of 50% by volume. The proof system in the United States is based on a scale where proof is calculated as twice the percentage of alcohol content. Therefore, if a beverage is labeled as 100 proof, it indicates that it contains 50% alcohol by volume. This system is designed for easy understanding; for example, 80 proof corresponds to 40% alcohol, and conversely, 120 proof would indicate 60% alcohol. The choice of 50% aligns with this established proof calculation and is essential knowledge for understanding and communicating alcohol content in the context of beverages.