If you want to weigh gold, it’s not as easy as it sounds. This is because gold in the form of coins, bars, or jewellery is almost never 100% pure. A piece of pure gold is soft and easily damaged, so it is combined with other metals to make it hard and durable. However, it is easy to weigh 1 ounce (28g) of gold once you know how to calculate the actual amount of gold that the object contains.
Find the percentage of gold in gold bars (bars or coins). The bars have information printed on the same metal. For coins, you will need to look up the specifications for it, which can be found in any catalogue that offers that specific type of currency. Once you know this proportion or percentage, use a precision scale to weigh the gold and then calculate the actual amount of gold. For example, if you have Krugerrands of gold, the percentage is standardized at 22 carats (91.67%). If you have 10 Krugerrands and you get 10,091 ounces (283g), simply multiply this by 91.67%. The result is that you have 9.25 ounces (262g) of gold.
Learn how to calculate the pennyweight of gold jewellery. The proportion of real gold in jewellery is given in carats, ranging from zero carats (zero gold content) to 24 (pure gold). Since jewellery is usually very small, jewellers express weight in “pennyweight” (abbreviated DWT). A pennyweight is equal to 1/20 of an ounce (1.4g) of gold.
Determine the amount of gold in a piece of jewellery. The first thing you need to do is find the jeweller’s mark to determine the number of carats. This can be very small, so occasionally you will need a magnifying glass to read it. If you are using a calculator, convert it to decimal notation by dividing the number of carats by 24. For example, for 18-carat gold, divide 18 by 24 to get 0.75 (the item is 75% gold).
Weigh gold jewellery using a precision scale like you would a gold ingot. Multiply the result by the percentage of gold in the object (from Step 3). Using the example in Step 3, if the jewellery weighs 0.4 ounces (11.3g), multiply 0.75 (the decimal equivalent to 18 carats) by 0.4 to get 0.30 ounces (8.5g) of gold.
Express the weight of gold in pennyweight jewellery. There is 20 pennyweight in one ounce (28g), so you simply multiply the weight by 20. In the example in Step 4, there are 20 times 0.30 ounces (8.5g), resulting in 6 pennyweights.