The cut, color, and clarity grades each have an effect on the value of a diamond, but the weight of the diamond has a significant effect on its value, too. The discerning buyer considers all four factors.

You're probably familiar with the term carat, the unit of measurement used to indicate the weight of gemstones. (This should not be confused with karat, the term jewelers use when stating the relative fineness of gold.)

You want to be sure your jeweler is clear about the terms that are used in reference to the weight of a diamond. One carat is equal to 1/5 of a gram. For diamonds less than one carat, weights can be expressed in terms of halves and quarters (as long as they are at least half or a quarter). For more precision, the carat can be divided into 100 points. Thus, a 10 point diamond is 1/10 of a carat.

Since small variations in weight can make big differences in price, you want to be sure that your diamond has been weighed in a precise and repeatable manner. AGS member jewelers weigh unmounted diamonds on an electronic scale capable of weighing as accurately as .002 (two one-thousandths) of a carat. No jeweler should be reluctant to show you how the weight of the stone you are looking at was arrived at.

The most important thing to know about weight is that weight isn't everything. You may come into your local jewelry store with a half carat or one carat stone in mind. That's fine. But you may be faced with a choice between a one carat stone of lesser value than a 90 point stone with higher grades for cut, color, and clarity. Sometimes less is more, even in the world of diamonds. Be flexible-you may get a more pleasing stone.

Of course, a well-cut, high grade, one carat diamond will certainly be more valuable than a similarly cut high grade 90 point stone. And, because of its rarity, a two carat well-cut highly graded diamond will be worth much more than twice what a one carat stone would cost.