Diamonds

The carat is the standard for diamond weight. A single carat is equal to 200 milligrams. When a diamond measures as less than one carat, a decimal expression is used to indicate what fraction of carat it is. It seems logical that the bigger the gem, the more you pay. And while this is true, diamonds have an especially steep price curve based on size, since larger diamonds are much harder to come by; they are typically found as smaller chips.

The demand for size also dictates the price. There's much higher demand for diamonds that are 1 carat or higher, which in turn drives up the cost since there's generally a set supply at any given time.

Some pieces have more than just one diamond. Pieces such as necklaces or bracelets may feature clusters of diamonds, each with a different weight. The carat classification has to be adjusted for this, so total carat weight, or TCW is put in place to note the total weight of the stones that are in the piece of jewelry.

There are some standards for reporting a diamond's weight. Federal Trade Commission guides allow a half-point of wiggle room in the stated weight of a diamond. For example, if you are looking at a diamond weighing .495 carats, legally it can be listed and sold as a 50 point diamond. But, in the case of a .494 carat diamond must be sold as a 49 point stone. Just bear that in mind as you shop, and pay attention to fine print.

Jewelers can set weight tolerance for diamond rings and jewelry and that's where the fine print comes in regarding diamond sizes. It may be in ads or flyers, and reads along the lines of, "all weights are approximate."

If a jeweler is practicing this, they are required by law to disclose it to the customer, which techically they are doing with that fine print. Read carefully. This mandate can also vary by state, which is important to keep in mind if you shop around in different states. Make sure you take notes on their weight structure to make sure you're truly comparing like stones.