Xignite provides spot metal prices data priced per troy ounce. Troy ounce is the global and traditional unit of weight used for precious metals, which was attributed to a weight used in Troyes, France, in medieval times.
1 troy ounce = 31.1034768 grams
1 ounce = 28.3495231 grams
1 troy ounce contains 2.75 grams more of metal than the standard ounce

The Xignite Global Metals API offers real time prices and quotes for metals including gold, silver, palladium, platinum and other base metals. In addition to real time precious metals prices, the service provides daily London Fixing prices as well as historical precious metal prices and metal news.