16 C.F.R. § 500.12
For bidimensional commodities (including roll-type commodities) measured in terms of commodity length and width, the declaration of net quantity of contents shall be expressed in the following manner:
(a) The declaration of net quantity for bidimensional commodities having a width of more than 4 inches (10.1 cm) shall:
(4) For any commodity for which the quantity of contents is required by paragraph (a) (2) or (3) of this section to include a declaration of the linear dimensions, the quantity of contents, in addition to being declared in the manner prescribed by the appropriate provisions of this regulation, may also include, after the customary inch/pound statement of the linear dimensions of the largest unit of measurement, a parenthetical declaration of the linear dimensions of said commodity in terms of inches.
(Example:“25 sq. ft. (12 in. × 8.33 yd.) (12 in. × 300 in.) 42.32 m 2 (30.4 cm × 7.62 m)”.)
(b) For bidimensional commodities having a width of 4 inches (10.16 cm) or less, the declaration of net quantity shall be expressed in terms of width and length in linear measure. The customary inch/pound statement of width shall be expressed in terms of linear inches and fractions thereof, and length shall be expressed in the largest whole unit (yard or foot) with any remainder in terms of the common or decimal fractions of the yard or foot, except that it shall be optional to express the length in the largest whole unit followed by a statement of length in inches or to express the length in inches followed by a statement of length in the largest whole unit.
(Example:“2 inches × 10 yards (5.08 cm × 9.14 m)”, “2 inches × 10 yards (360 inches) 5.08 cm × 9.14 m”, or “2 inches × 360 inches (10 yards) 5.08 cm × 9.14 m”.)