27 CFR §5.202

1. (a)General. Except as provided in paragraph (d) of this section and in § 5.205, distilled spirits must be bottled in standard liquor containers, as defined in this paragraph. A standard liquor container is a container that is made, formed, and filled in such a way that it does not mislead purchasers as regards its contents. An individual carton or other container of a bottle may not be so designed as to mislead purchasers as to the size of the bottle it contains.
2. (b)Headspace. A filled liquor container of a capacity of 200 milliliters (6.8 fl. oz.) or more is deemed to mislead the purchaser if it has a headspace in excess of 8 percent of the total capacity of the container after closure.
3. (c)Design. Regardless of the correctness of the stated net contents, a liquor container is deemed to mislead the purchaser if it is made and formed in such a way that its actual capacity is substantially less than the capacity it appears to have upon visual examination under ordinary conditions of purchase or use.
4. (d)Exception for distinctive liquor bottles. The provisions of paragraphs (b) and (c) of this section do not apply to liquor bottles for which a distinctive liquor bottle approval has been issued pursuant to § 5.205.