fluid ounce (US) [fl oz (US)] Unit Converter

Definition of fluid ounce (US) [fl oz (US)] unit

The US fluid ounce (fl oz) is a customary unit of volume equal to 1/128 of a US liquid gallon, exactly 29.5735295625 milliliters, or approximately 1.8047 cubic inches. It measures liquid capacity, not mass.

History of fluid ounce (US) [fl oz (US)] unit

The US fluid ounce developed from English volume measures used in colonial America, but it diverged from the British Imperial fluid ounce after national standards evolved. In 1824, Britain standardized its gallon around water’s mass, producing an Imperial fluid ounce of 28.413 milliliters. The United States retained an older wine-gallon basis: 231 cubic inches, divided into 128 fluid ounces. This relationship became part of customary measurement practice, while later metric conversion defined the US fluid ounce precisely as 29.5735295625 milliliters. The unit remains legally recognized in labeling contexts.

Applications of fluid ounce (US) [fl oz (US)] unit

The US fluid ounce is commonly used for beverages, cooking ingredients, medicines, cosmetics, and household liquids. Beverage containers may list servings in fluid ounces, while recipes use the unit for oils, milk, or syrups. In the United States, nutrition labels express liquid serving sizes in fluid ounces, often alongside milliliters for international clarity.

Complete list of fluid ounce (US) [fl oz (US)] unit conversion