Museo Galileo
Virtual Museum

The term was introduced by the ancient Greeks, who, having a duodecimal-base system, used the word to denote a small value equal to one-twelfth of a unit of length or weight. The Romans adopted the concept as well, calling it uncia and applying it to the same purposes. Identically-named units of weight and measurement would be assigned different values depending on the locality. As the "ounce" consistently referred to one-twelfth of the measure chosen as the unit (foot, palm, or arm, according to the region), its value varied from town to town. "Square ounces" and "cubic ounces" were used for measuring surface areas and volumes respectively. This situation persisted until the adoption of the decimal metric system. Since then, the term "ounce"—in countries where it is no longer used as a unit of measurement—has taken on the meaning of "small quantity."