The abbreviation "DWT" in jewelry means "pennyweight." A pennyweight is a unit of mass equal to 24 grains, 0.05 troy ounce or 1.56 grams. Jewelers and gold buyers use pennyweights or grams to weigh gold and other precious metals.
A gold buyer who is using pennyweights to measure an amount of scrap gold must multiply it by its percentage of purity divided by 100. For example, 18k gold is 75 percent gold, so the weight in 18k gold would be multiplied by 0.75. Then, the gold buyer divides this weight by 20 to determine the weight of the gold in troy ounces and multiplies it by the spot price of gold to determine its value.