Weight. What is a Carat?

Diamonds are sold by the carat (CT), not to be confused with Karat (KT), which in the United States refers to gold quality. Since 1913 most countries have agreed that a carat weighs 200 milligram, or 1/5 gram. Before 1913 the carat weight varied depending upon the country of origin, the Indian carat didnt weigh the same as the English carat; the French carat was different from the Indian or the English. This is important if you have, or are thinking of buying , a very old piece that still has the original bill of sale indicating carat weight; the old carat weighted more than the new, post 1913 metric carat, which is 200 milligram (1/5 gram). Therefore, an old three carat stone will weigh more than three carats by the new standards. Today the term carat means the metric carat, the 200 milligram carat. There are five carats to one gram.

Jewelers often refer to the carat weight of diamonds in terms of points. This is particularly true of stones under one carat. There are 100 points to a carat, so if a jeweler says that a stone weighs 75 points, that means it weigh 75/100 of a carat, or 3/4 carat. A 25 points stone is 1/4 carat. A 10 points diamond is 1/10 carat.

The carat is the unit of weight, not size. I wish to stress this point, since most people think that a one carat stone is a particular size. Most people, therefore, would expect a one carat diamond and one carat emerald, for example, to look the same size or to have the same apparent dimensions. This is not true.

Comparing a one carat diamond to a one carat emerald and a one carat ruby easily illustrate this point. First, emerald weighs less than diamond and ruby weighs more than diamond. This means that a one carat emerald will look larger than a one carat diamond, while the ruby will look smaller than a diamond of the same weight. Emerald, with a mineral composition that is lighter, will yield greater mass per carat; ruby, with its heavier composition, will yield less mass per carat.

Equal volumes of materials with the same density, however, should have approximately the same weight, so that in diamond, the carat weight has come to represent particular sizes. These sizes are based on diamonds cut to ideal proportions.

How does carat weight affect value in diamonds?

Diamond prices are usually quoted per carat. Diamonds of finest quality are sold for the highest price per carat, and diamonds of progressively less fine quality are sold for a progressively lower price per carat. Also, as a rule, the price increases per carat as we go from smaller to larger stones, since the larger stones are more limited in supply. furthermore, stones of the same quality weighting exactly one carat will sell for much more than stones weighting 90 to 96 points. Thus, if you want a one carat diamond of a particular quality, but its cost goes over your budget, you may find one in a 95 point diamond more affordable, and a 95 point diamond will give the impression of a full one carat diamond when set. You might be able to get your hearts desire after all.

The price of a diamond does not increase proportionally; there are disproportionate jumps. The larger and finer the stone (all else being equal in terms of overall quality), the more disproportionate the increase in the cost per carat may be. A top quality two carats diamond will not cost twice as much as a one carat diamond, it easily be four times as much.

What is spread?

The term spread is often used in response to the question How large is this diamond? But it can be misleading. Spread refers to the size the stone appears to be, based o its diameter. For example, if the diameter of the stone measured the same as you see in the diamond sizes chart (shown above) which represents the diameter of a perfectly proportioned stone, the jeweler might say it spreads one carat. But this does not mean it weight one carat. But this does mean it weights one carat. It means it looks the same size as a perfectly cut one carat stone. It may weigh less or more, usually less.

Diamonds are generally weighted before they are set, so the jeweler can give you the exact carat weight, since you are paying a certain price per carat. Note, also, that the price per carat for a fine stone weighting 96 points is much less than for one weighing one carat or more. So it is unwise to accept any approximate weight, even though the difference seems so slight.

It is also important when buying a diamond to realize that since carat refers to weight, the manner in which a stone is cut can affect its apparent size. a one carat diamond that is cut shallow will appear larger in diameter than a stone that is cut thick (heavy). Conversely, a thick diamond will appear smaller in diameter.

Furthermore, if the diamond has a thick girdle, the stone will appear smaller in diameter. If this girdle is faceted, it tends to hide the ugly, frosted look of a thick girdle, but the fact remains that the girdle is thick, and the stone suffers because it will appear smaller in diameter than one would expect at a given carat weight. These stones (diamonds) are therefore somewhat cheaper per carat.