Afifth is aunit ofvolume formerly used forwine anddistilled beverages in the United States, equal to one fifth of aUS liquid gallon, or25+3⁄5U.S. fluid ounces (757milliliters); it has been superseded by themetric bottle size of 750 mL,^[1] sometimes called ametric fifth, which is the standard capacity ofwine bottles worldwide and is approximately 1% smaller.

Before the mid-19th century, the capacity of British alcohol bottles used for wine and distilled liquors was nominally a quart, but the actual capacity varied considerably. Four primary styles existed, with different average capacities: 759 ± 27 mL (715–810 range); 781 ± 47 mL (724–880); 808 ± 49 mL (739–835); and approximately 1130 mL, the "imperial wine quart". Beer and cider bottles had a different range of sizes.^[2] In 1842, it was reported that ordinary wine bottles were 1/6 of an imperial gallon, that is, 758 mL.^[3]

After its independence, the United States continued some British measures, but altered others (e.g., theU.S. liquid gallon). In the late 19th century, liquor in the U.S. was often sold in bottles which appeared to hold one US quart (32 US fl oz; 950 mL), but in fact contained less than a quart and were called "fifths",^[4] "short quarts",^[5] orcommercial quarts.^[6] At this time, 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,^[6][7][8]and thus the difference between adrinking saloon or barroom and a dry-goods store.^{[citation needed]}

The fifth was the usual size of bottle for distilled beverages in the United States until 1980.^[9] Other authorized units based on the fifth included4⁄5 pint, called atenth, and1⁄10 pint.^[10]During the 1970s, there was a push formetrication of U.S. government standards. In 1975, theBureau of Alcohol, Tobacco and Firearms, in cooperation with theDistilled Spirits Council of the United States, proposed metric-standard bottle sizes to take effect in January 1979, with a one-year changeover period in which both sets of sizes were legal; these standards were incorporated intoTitle 27 of theCode of Federal Regulations.^[10][11] These new sizes were 50 mL (aminiature), 100 mL, 200 mL, 375 mL (355 mL for cans), 500 mL (discontinued for distilled beverages in June 1989, but not for wine),^[12] 750 mL (the usual size of a wine bottle), 1 liter, and 1.75 liter (ametric half-gallon or "handle"). Wine also has a standard 187 mL (6.6 imp fl oz; 6.3 US fl oz) measure and uses 1.5 liters (amagnum) instead of 1.75.^{[citation needed]}

• Alcohol measurements