Diamond weight is measured in carats, a small unit of measurement equal to 200 milligrams. Each carat is divided into 100 points. Therefore, a half-carat stone may be referred to as a "50-pointer" or "50-points". Carat weight is the easiest of the 4 C's for gemologists to determine because of the use of sophisticated measuring equipment.

Two diamonds of equal carat weight might vary greatly in value depending upon their cut, color and clarity. This is important because when mounted, one diamond may appear larger than the other, although they actually weigh the same. Because large diamonds are rare, they generally have a greater value per carat. For example, the price of a two-carat stone will be several times higher than four 50-pointers of equal quality.

For an easy comparison of price and size, see the illustration below. Prices are approximate and based upon an ideal cut, G Color, VS2 clarity, diamond:

Approximate Starting Price: 0.50ct 0.75ct 1.00ct 1.50ct 2.00ct 5.2mm 5.8mm 6.5mm 7.4mm 8.2mm

Determining the Carat Weight that's Right for Her

Determining the carat weight that is right for her is a simple choice. Consider the size of her fingers. If she has a fairly small ring size, a smaller diamond will look proportionate on her hand. Find a moderate balance between the color and clarity grades to see how much carat weight you can get for your budget. Also, bear in mind the width of your engagement setting. Find a carat weight that complements the setting nicely without overpowering it, and vice versa.