If you've ever weighed a one ounce bullion bar or coin then you might have noticed that it weighs more than one ounce. But it's not an error. Silver, gold, and platinum are measured in troy ounces rather than ounces.
The standard ounce, also known as the avoirdupois ounce, is what everyone is used to. It's commonly used in markets to measure all different types of goods. The only exceptions are silver, gold, platinum, and gunpowder which are measured in troy ounces. One troy ounce is equal to 1.0971 ounces. A troy ounce is equal to 31.1035 grams. An ounce is equal to 28.3495 grams.
Troy weights date back to Ancient Rome. The Romans used the troy ounce to measure silver, gold, platinum, and gunpowder and their weight standards are still used today for those commodities. It was easier to maintain the troy ounce standard rather than change over to avoirdupois ounces.
The troy ounce uses the abbreviation t oz. The avoirdupois ounce uses the abbreviation oz. If you are in the market to buy silver bullion then you should look closely to see whether an item is weighed in troy ounces or ounces. The large bullion retailers will always list troy ounces. However a random seller on eBay may use ounces so you need to be careful. You wouldn't want to buy an item weighed in ounces when you assumed that it was weighed in troy ounces.
1 troy ounce = 1.0971 ounces
1 troy ounce = 31.1035 grams
1 troy ounce = 480 grains
1 troy ounce = 0.0686 pounds
1 troy ounce = 0.0833 troy pounds
1 troy ounce = 20 pennyweights