Fifth (unit)

A fifth is a unit of volume formerly used for distilled beverages in the United States, and is equal to one fifth of a gallon, 4⁄5 quart, or 253⁄5 fluid ounces (757 mL); it has been superseded by the metric fifth of 750 mL (26 imp fl oz; 25 US fl oz), approximately 1% smaller, which is the normal capacity of wine bottles world-wide.

The fifth was the usual size of bottle for whisky in the United States until 1980. During the 1970's, there was a push for metrication of U.S. government standards, and the United States Code was amended to require metric standards of fill for distilled spirits.