There are approximately 29.574 milliliters (mL) per US liquid ounce (fl. oz). To convert a volume measurement in ounces to milliliters, simply multiply it by 29.574.
Ounces that measure volume are called fluid ounces. They are part of the imperial system of measurement, while milliliters are a metric unit of measurement. Fluid ounces are widely used in the United States, one of the few countries that still operates primarily on the imperial system. Most countries have adopted the metric system, which measures volume primarily with liters. A milliliter is equal to exactly one-thousandth of a liter. Volume can also be measured with cubic meters or a related unit with the metric system.
As of 2014, the United States is the only industrialized country that does not use the metric system as a standard form of measurement. The wine and liquor industries in the United States converted to the metric system following the passage of the Metric Conversion Law in 1975. Other instances in which the metric system has become more common in the United States include the measurement of medications, specifications for cameras and other electronic devices, and nutrition labeling on food.