sentences:  Proof (the term "degrees proof" is not used), defined as twice the percentage of alcohol by volume, may also be stated.For example, whiskey may be labeled as containing 50% alcohol by volume, and also as 100-proof; 86-proof whiskey contains 43% alcohol.The Code of Federal Regulations (27 CFR [4-1-03 Edition] §5.37 Alcohol content) requires that liquor labels must state the percentage of ABV.