Carat is a measurement of weight for gemstones. A carat equates to 0.20 grams. Diamonds are weighed to one-hundredth of a carat and this weight directly affects the diamond's value e.g. diamonds of a heavier weight are usually considered to be of higher value (of course this is dependant upon the other Cs!). Diamonds are often referred to in terms of points. In every carat there are 100 points, therefore a 75 point diamond is 0.75 carat (three quarters of a carat). If you are concerned about the cost of several gemstones the carat weight can be a good point of comparison. High street jewellers regularly supply gemstones of 0.05 -1 carat in weight.
The carat weight of a diamond can (in rough terms) be equated to a size. A diamond that weighs 1.5 carat in a brilliant cut will usually measure approximately 6.5mm in diameter. Many jewellers are able to provide customers with a stencil gauge of diamond sizes and carat weights to give a visual suggestion of what your diamond will look like at a particular carat weight. Of course when comparing the dimensions of a diamond against its carat weight you must consider the proportions of the cut. If for example a diamond is cut a little deeper than normal then its dimensions will not equate with what a stencil gauge will suggest as the width of the stone will be less than expected, whereas a stone that is wider than normal but of the same carat weight will be shallower than is standard.
This is by no means a precise tool, however it can still be very helpful when helping customers make a decision by getting a visualisation of its physical size. Of course this means if for example a customer presents you with a piece of jewellery of their own and they are unsure of the carat weight you should be able in simple terms, to estimate its approximate carat weight by measuring its size. There are some tools with built in tables for this function also, as well as some more complex formulas to estimate the carat.
The carat weight of a stone should be measured before the gemstone is set, in order to give an accurate account of the piece of jewellery, it will be measured using specialist gemstone scales. When selling a piece of jewellery the customer should have a full account of the details of the piece with information such as the metal type, carat, gemstone type, cut and in the case of a diamond its specifications are known as the 4 c's - carat, cut, clarity and colour.
Of course today there is what is known as the 5th C. This is a diamond certificate or grading report which is an assessment of a diamond which details all of its qualities discussed above. It is performed by an independent laboratory or institution such as the IGI or EGL. It can provide a customer with assurance and confidence in their choice as well as providing you with a document for financial purposes. There has been growing interest in this additional option for customers and it is regularly available of diamonds of 0.50ct or higher weight. This can be a lovely option to go for when choosing your diamond engagement ring it will give you some independent assurances of the quality and features of your diamond.