A 100% pure gold is said to be pure when it consists of 24 karats. Conversion into the percentage of gold using gold karat: Once you recognise the karats of your gold jewellery, it’s best to convert them to a proportion so as to work out what part of the gold alloy you have got is truly pure gold. This calculation is straight forward: simply divide the Karat variety of your jewellery by number 24 and multiply by 100. For example, if you have got determined that a gold item with you is 18 karats, dividing that by 24 provides you 0.75, that is up to 75th gold content. To determine the purity amount of gold. Multiply the weight of the jewellery in grams by its purity. Example: you brought 18 Karat gold ring which weighs 10 grams, but you know 18 Karats is equal to 75% purity. Now you can calculate 75% of 10 grams, that equals to 7.5 grams pure gold. Calculating the load of Pure Gold in Ounces and Troy Ounces 1 troy ounce = 31.1 grams and 1 ounce = 28.34 grams. To convert your gold from grams to ounces, you got to divide it by 28.34 and for troy ounce divide it by 31.1. Example: you brought 10 grams gold, so the ounce would be 0.35 ounces and a troy ounce would be 0.32 troy ounces.