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A Guide to Carats and diamond sizes

The timeless beauty of diamonds has spanned the ages, their sparkle and capture of light beguiling all who encounter them. If considering a purchase of such sublime gemstones as diamonds, it is worthwhile doing some research before making an investment. This guide provides all the information needed on carats and diamond sizes to assist in making the right decision.

Originally, the carob seed was the old unit of measurement for diamond traders and from where the word carat is derived, but what is a carat? A carat is the modern standard unit of weight for gemstones, including diamonds, and the underpinning principle to bear in mind is the higher the carat weight, the bigger and more expensive the diamond. Larger diamonds are extremely rare, to the degree that it is estimated fewer than one in one million rough diamonds are of adequate size to produce a finished one carat diamond, hence their high cost.

As well as the carat weight, there are several other factors to consider in selecting diamonds which are equally important.

To gain perspective on how carat weights relate to the size of diamonds, the following examples should be considered.

A carat is the equivalent to 200 milligrams in weight, therefore a five carat diamond weighs one gram and a 2268.2 carat diamond would weigh one pound. This would be a very precious gemstone indeed.

Points are also used as a method of measuring diamond weight, with 100 points making up one carat. An example of this would be 0.2 carats the equivalent of 20 points. [source:jewelrynotes.com]

The biggest diamond in the world is known as the Cullinan diamond, named after the owner of the South African mine. It weighed more than 3106 carats and earned the title of the biggest diamond due to its 600 gram mass.

An important consideration is the distance across the top of a diamond, as this is how the diamond stone is viewed, for example, when set in a ring. Distance is measurable in millimetres and the quality of the cut should be factored into any decision to purchase. The quality of the cut grade cannot be over-emphasised as it is those diamonds cut with the correct proportions and symmetry which give optimal sparkle, allowing light to reflect from the top of the diamond. If a diamond is cut inexpertly, the carat weight can be concealed towards the diamond's base. Crucially, the effect of this would make the diamond carat size appear smaller than its true carat weight.

Another element to consider is that not all diamonds of the same carat weight are necessarily equal, and it is important to take into account the depth and shape of the diamond. If a comparison was made between two one carat diamonds, each diamond may differ in millimetre width. A quality, one carat diamond should measure in a range of 6.4 millimetres to 6.5, a three carat diamond 8.10 millimetres and a 0.2 cts stone 4.10 millimetres. However, it should be noted that, within measurement parameters, every diamond remains unique.

Based on the link between diamond carat weight and price, there are a series of weights that denote an increase in cost once these particular weights are met. The series ranges from 1/2 carat through to one carat up to two carats and are referred to as magic or popular weights. Up to 30% can potentially be saved on the cost of a diamond if an under-size is purchased. There is no suggestion that an under-size diamond is deficient in quality, rather that if someone were to purchase a 2 carat diamond, a significant saving could be made if they opted for a 1.9 carat weight diamond instead. 

It is worth spending a little time determining the principles of weight, depth and cut-grade in order to make the perfect choice for such a special purchase. This will ensure the selected diamond offers a unique signature of elegance and refinement to be enjoyed for a lifetime.


Other diamond quality factors: