What are Troy Ounces?
A troy ounce is the unit gold, silver and platinum prices are quoted in. It is about 10% heavier than an avoirdupois ounce, but a troy pound has only 12 of them.
One troy ounce is equivalent to approximately 31.1035 grams, which is about 10% heavier than a standard avoirdupois ounce. The term "troy" originates from the city of Troyes in France, where this unit of measurement was historically used in the trade of precious metals.
What are pennyweights?
Pennyweights are a unit of measurement commonly used in the jewelry industry to measure the weight of precious metals such as gold and silver.
A pennyweight is 1/20th of a troy ounce, which is 1.55517 grams. Jewelers still use it for small amounts of gold and silver.
To get grams from pennyweights multiply by 1.555 – 10 pennyweights is about 15.55g. The abbreviation dwt comes from d for denarius, the old penny.