The common standards of weight measurement for gold are either grams or pennyweights . There are 20 pennyweights in one ounce, with 12 ounces making a pound and there are 28 grams to an ounce. If you are unfamiliar with one of these measurements, simply convert them. If you are presented with gram weight, multiply each gram by 0.643 and you will have the pennyweight. If you are presented with pennyweights, reverse the equation and you will have grams. Weight indicates the amount of pure gold you have bought, relative to the total weight of the piece, and this will give you some idea as to the price you should be paying.
The easiest misconception to correct about gold is the confusion between karat weights [abbreviated to K or KT] and carat weights [abbreviated to ct.]. Carat weights are used to weigh gems and nothing else. This is a particular system which literally translates to 200 milligrams or one-fifth of a gram per metric carat. Anything less than one whole carat is measured in points, as there are one hundred points to a whole carat. Thus a 50 point carat diamond, for example, is actually a ½ carat diamond, a 75 point diamond is really a ¾ carat diamond, and so forth. Gold, on the other hand, is weighed in karats, which refers to the gold content among the alloy mix in any give piece of jewelry. They are essentially the same in terms of being standards of measurements, but the two beginning letters have been changed to avoid confusion. In other parts of the world besides the U.S there are other systems for evaluating gold. In Italy and many other European countries, for example, gold is measured in 1000-part units. One thousand Italian units of gold translate into 24K in the States, 833 units translate into 20K, and 750 units are 18K and so forth.
All gold jewelry should be tagged with the karat content, so that you may know what you are buying. As this measurement system has its origins in ancient times, and later on was used in the Byzantine era, today's gold is measured in the same traditional method. The ‘solidus' gold coin of the Byzantine era was comprised of 24 parts [called 24 karats or ‘keration'] and today gold is also evaluated as a 24 part alloy. Thus 24 karat gold refers to utterly pure gold; 1 karat means 1/24 part gold, 12 karat gold is 50% pure gold mixed with 50% of other metals, and so forth. The set minimum for gold content in any alloy varies from country to country. In France and Italy , where gold purity is taken very seriously, the minimum gold content is 18K. Less than that and the piece isn't considered to be gold. The U.S, England and Canada have less restrictive standards and jewelry is considered to be gold if the gold content is above 9 or 10 karats.