16 C.F.R. § 500.21 – Type size in relationship to the area of the principal display panel.

(a) The statement of net quantity of contents shall be in letters and numerals in a type size established in relationship to the area of the principal display panel of the package or commodity and shall be uniform for all packages or commodities of substantially the same size. For this purpose, “area of the principal display panel” means the area of the side or surface that bears the principal display panel, exclusive of tops, bottoms, flanges at tops and bottoms of cans, and shoulders and necks of bottles and jars. This area shall be:
1. (1) In the case of a rectangular package or commodity where one entire side properly can be considered to be a principal display panel side, the product of the height times the width of that side;
2. (2) In the case of a cylindrical or nearly cylindrical container or commodity, 40 percent of the product of the height of the container or commodity times the circumference; and
3. (3) In the case of any otherwise shaped container or commodity, 40 percent of the total surface of the container or commodity: Provided, however, that where such container or commodity presents an obvious “principal display panel” such as the top of a triangular or oval shaped container, the area shall consist of the entire top surface.
(b) With area of principal display panel defined as above, the type size in relationship to area of that panel shall comply with the following specifications:
1. (1) Not less than 1/16 inch (1.5 mm) in height on packages the principal display panel of which has an area of 5 square inches or (32.2 cm ²) less.
2. (2) Not less than 1/8 inch (3.1 mm) in height on packages the principal display panel of which has an area of more than 5 (32.2 cm ²) but not more than 25 square inches (161 cm ²).
3. (3) Not less than 3/16 inch (4.7 mm) in height on packages the principal display panel of which has an area of more than 25 (161 cm ²) but not more than 100 square inches (6.45 dm ²).
4. (4) Not less than 1/4 inch (6.35 mm) in height on packages the principal display panel of which has an area of more than 100 square inches (6.45 dm ²), except not less than 1/2 (12.7 mm) inch in height if the area is more than 400 square inches (25.8 dm ²).
(c) Where the statement of net quantity of contents is blown, embossed, or molded on a glass or plastic surface rather than by printing, typing, or coloring, the lettering sizes specified in paragraph (b) of this section shall be increased by 1/16 of an inch (1.5 mm).
(d) Letter heights pertain to upper case or capital letters. When upper and lower case or all lower case letters are used, it is the lower case letter “o” or its equivalent that shall meet the minimum standards.
(e) The ratio of height to width of a letter shall not exceed a differential of 3 units to 1 unit (no more than 3 times as high as it is wide).
(f) When fractions are used, each component shall meet one-half the minimum height standards.
(g) The type size requirements specified in this section do not apply to the “e” mark. (See § 500.6(b).)
(h) When upper and lower case or all lowercase letters are used in SI metric symbols, it is the uppercase “L,” lowercase “d,” or their equivalent in the print or type used that shall meet the minimum height requirement. Other letters and exponents must be presented in the same type style and in proportion to the type size used. However, no letter shall be less than 1.6 mm ( 1/16 inch) in height.