Code of Federal Regulations Title 27. Alcohol, Tobacco Products and Firearms § 27.5.37 Alcohol content

(1) Mandatory statement. The alcohol content for distilled spirits shall be stated in percent–alcohol–by–volume. Products such as “Rock and Rye, or similar products containing a significant amount of solid material shall state the alcohol content at the time of bottling as follows:  “Bottled at ___ percent–alcohol–by–volume.”

(2) Optional statement. In addition, the label may also state the alcohol content in degrees of proof if this information appears in direct conjunction (i.e. with no intervening material) with the statement expressed in percent–alcohol–by–volume. If both forms of alcohol content are shown, the optional statement in degrees of proof shall be placed in parentheses, in brackets, or otherwise distinguished from the mandatory statement in percent–alcohol–by–volume to emphasize the fact that both expressions of alcohol content mean the same thing.