There exists a lot of different units for measuring weight, pounds, ounces, kilos, grams and so on. In other words we have various systems for measuring, metric and imperial being the two which are most used. When it comes to precious metals the situation is even more complicated because there exists even more division, you have troy ounces, avoirdupois ounces, grains, pennyweights and so on. In this text I’m gonna focus on explaining what exactly is a pennyweight and how to calculate weight of a certain precious metal piece in pennyweight.
One pennyweight is equal to 0.05 ounces, troy ounces to be more precise, its symbol is dwt. Majority of gold isn’t pure, for reasons that were mentioned before, and I don’t want to repeat them here, look it up in previous posts. This means that if you want to say how much gold there is in a certain jewelry piece made from gold and you want to express that weight in pennyweights, you need to get ready to do some calculations. First thing that you have to do is to find out how pure the piece is. For this demonstration I’m gonna presume that jewelry piece has 18 karats. 18 karats means that only 75% of jewelry is actually gold, the rest consists of other metals. You get this number by dividing the purity of the piece with 24, which is the maximum number of karats that a precious metal can have, 24K signifies 100% purity, or purity very close to 100%. If for example you had 14K gold, you would divide 14 with 24, which is somewhere around 58%. When you divide these numbers you don’t get percentages right away, you get 0.75 and 0.5833, for 18K and 14K respectively, and to get percentages I’ve multiplied these numbers with 100, you don’t have to do that. For calculations that we’re gonna do, these decimal numbers are perfect, in fact that’s what we need. Now that you have 0.75 you’re gonna have to find out what’s the total weight of the piece that you’re interested in. It would be great if you had a scale which measures pennyweights directly, but if you cannot find one don’t worry, you can use one that measures ounces, but be careful that it measures troy ounces, not avoirdupois ounces, there’s a difference between these two, they’re not the same.
When you’ve done weighing the item, and you know how heavy the 18K gold piece is, then you’re ready for some more calculation, yey, don’t worry it’s nothing too complicated, anybody can do it. If you’ve weighed the piece with the help of a pennyweight scale, all that you have to do is to simply multiply the number that you got with 0.75, 0.75 if you have 18K jewelry. So if for example you have 79 dwt, you have to multiply 79 with 0.75, which is 59.25, and you know that there is 59.27 dwt, in your jewelry piece. Remember, dwt is the symbol for pennyweight.
If you cannot weigh directly in pennyweight, or if you already know what the weight of your piece is in troy ounces, then worry not, because it’s easy to convert ounces into pennyweight. If for example the item for which you’re calculating the gold content has 3 troy ounces, then in order to calculate how much its weight in pennyweight is you have to divide these 3 troy ounces with the previously mentioned 0.05, which is how much ounces 1 dwt contains. 3/0.05 is 60, and now that you know that, you just repeat what we did before, multiply 60 with 0.75, and you know how much gold there is in your 18K jewelry, and not only that you know how much gold there is in pennyweight;).