<P> A fifth is a unit of volume formerly used for distilled beverages in the United States, equal to one fifth of a US liquid gallon, ⁄ quart, or 25 ⁄ US fluid ounces (757 ml); it has been superseded by the metric bottle size of 750 ml, sometimes called a metric fifth, which is the standard capacity of wine bottles world - wide and is approximately 1% smaller . </P> <P> In the late 19th century, liquor was often sold in bottles which appeared to hold a quart 32 US fl oz (950 ml) but in fact contained less than a quart and were called "fifths", or commercial quarts . </P> <P> One fifth of a gallon was a common legal threshold for the difference between selling by the drink and selling by the bottle or at wholesale, and thus the difference between a drinking saloon or barroom and a dry - goods store . </P> <P> The fifth was the usual size of bottle for distilled beverages in the United States until 1980 . Other authorized units based on the fifth included ⁄ pint and ⁄ pint . </P>

Where did a fifth of alcohol come from
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