16 C.F.R. § 500.10
(b) Declaration of net quantity of contents in terms of fluid measure shall be identified as such in each instance and the statement of U.S. gallon of 231 cubic inches and quart, pint, and fluid ounce subdivisions thereof shall be expressed as follows:
(3) If 1 gallon or more, in terms of the largest whole unit (gallons followed by common or decimal fractions of a gallon or by the next smaller whole unit or units viz, quarts and pints) with any remainder in terms of fluid ounces or common or decimal fractions of the pint or quart, except that it shall be optional to include an immediately adjacent additional expression of net quantity in terms of fluid ounces.
(Examples:“Net contents 2 1/2 gal. (9.46 L)”, “Contents 2.5 gal. (9.46 L)”, or “Net contents 2 gallons 2 quarts (9.46 L)” but not as “2 gallons 4 pints (9.46 L)”.)