The troy ounce is a specific unit of mass preserved for use in specialized, high-value markets, distinct from standard measurements used in everyday commerce. Its usage ensures consistency and accurate valuation in global financial markets. This specialized unit differs significantly from the ounce most people encounter when weighing common goods.
The Precise Gram Conversion
A troy ounce (ozt) is precisely equal to 31.1034768 grams (g). This exact numerical value is the standard used for official transactions in the commodities markets worldwide. For quick, general reference, a troy ounce is often rounded to 31.1 grams.
Defining the Troy Ounce
The troy ounce is a unit within the historical troy weight system. Its abbreviation is typically written as “ozt” or “oz t” to distinguish it from the common ounce. The system is widely believed to have originated in the medieval European trading hub of Troyes, France. Merchants at the large trade fairs in Troyes needed a standardized, reliable weight to facilitate commerce, leading to the adoption of the troy system.
The troy system is built upon a smaller unit called the grain, with one troy ounce equaling 480 grains. This weight system was officially adopted for gold and silver coinage. While other troy weight units, like the troy pound, have largely fallen out of use, the troy ounce remains the sole unit from the system still in common use today.
The Difference Between Troy and Avoirdupois Ounces
The primary source of confusion stems from the existence of two different ounces: the troy ounce and the avoirdupois ounce. The avoirdupois ounce is the standard unit of mass used for nearly all everyday items, such as groceries, dry goods, and general shipping. This common avoirdupois ounce weighs approximately 28.3495 grams.
The troy ounce, by contrast, is heavier than the avoirdupois ounce. The difference between the two is roughly 2.75 grams, which makes the troy ounce about 9.7% to 10% heavier than the standard ounce.
The distinction is further complicated when comparing the respective pounds in each system. An avoirdupois pound is made up of 16 avoirdupois ounces, whereas a troy pound consists of only 12 troy ounces. Consequently, while the troy ounce is heavier than the avoirdupois ounce, the troy pound (373.24 grams) is actually lighter than the standard avoirdupois pound (453.59 grams).
Industries That Utilize the Troy System
The troy ounce is maintained as the global standard almost exclusively for measuring precious metals, including gold, silver, platinum, and palladium. When the price of these metals is quoted on commodity exchanges, the reference is always to the price per troy ounce.
The continued use of this older system provides a standardized measurement that ensures consistency across international markets. For example, a gold bar stamped with its weight in troy ounces is guaranteed to contain that precise mass, regardless of the country of origin. This universal standard simplifies international commerce and eliminates potential weight-related trade disputes over high-value goods.