A fluid ounce is a form of measurement that is commonly used in U.S. and British measuring systems. An ounce is equal to 30 milliliters and a fluid ounce is used only to measure liquids. Throughout history, there have been many definitions of an ounce. It was primarily used in England and in Scotland to measure both wine and water. When it was used to measure these things, the measurement of the ounce varied depending on the liquid that was being measured. For example, an ounce of ale would be a different amount of liquid than an ounce of wine.
The fluid ounce that is used in the U.S. is somewhat different than the ounces that are used in Britain. The fluid ounce is around 4 percent larger than the imperial ounce that is commonly used in Britain. The fluid ounce is based on U.S. gallons, which are slightly different than gallons that are used in the imperial system of England. Unlike the ounces in Britain, the U.S. fluid ounces make up 29.57 milliliters, instead of exactly 30.Learn more about Measurements