It's As Easy As the 4Cs: How to Buy a Diamond Engagement Ring

Familiarize yourself with a diamond's 4Cs—cut, color, clarity, and carat weight—and make your purchase with another C word: confidence.

Not to be confused with shape, a diamond's cut refers to the way it reflects light—or, put simply, how dazzling it is. The Gemological Institute of America (GIA), an organization that identifies and grades diamonds, rates cuts on a sliding scale, from excellent all the way down to poor. The more skillful that cut is, the better the sparkle, so be sure to request a diamond's GIA report before you buy it. "Even if a diamond has perfect color and clarity, a poor cut can make it look dull," says Josh Holland of online jewelry retailer Blue Nile.

Found naturally in a spectrum of shades, diamonds are rated on an alphabetical scale from colorless (D) to brown (Z). It's no surprise that Ds are the most expensive within that range, but even if you're not exactly on a Beyoncé budget, you can take a deep breath.

"Stones in the G to I range have little or no noticeable color, which makes them a great value," says Holland. On the other hand, when a stone is so deeply hued that it would register off the charts, like the yellow one shown here, it's called "fancy." In those extreme cases, color is a good thing that results in a very rare (and costly) diamond.

Stones can have two types of imperfections: blemishes, which are on the outside, and inclusions, found on the inside. The more flaws, the lower the clarity rating. Still, most defects are so small that they can be seen only under magnification. And since near-flawless specimens can be prohibitively pricey, Holland suggests selecting an "eye-clean" diamond, whose tiny specks are visible only under a microscope.

All gems are weighed in metric carats, and each carat is composed of 100 points. So a 50-point diamond weighs .5 carats, a 75-point stone is .75 carats, and so on. That said, carat refers to weight, not size. Translation? How large a stone looks isn't always representative of how much it weighs.