NEW YORK — Buying a diamond ring can be intimidating. What do you look for? How much should you pay? Should you buy online or in a store? Demystify the process by learning about the four C’s: carat, color, clarity and cut. This system of grading diamonds was developed 60 years ago by the Gemological Institute of America.

Then do research online or visit jewelers. You’ll soon understand the options. Here’s a primer on the four C’s.

The four C’s

Carat is a weight measurement. A 1-carat diamond weighs 200 milligrams. But there’s no ideal size for a diamond. It depends on your budget and taste. Some women want a big rock; others prefer a delicate, less blingy look.

Small diamonds are cheaper than large diamonds. A ring with three small diamonds totaling 1 carat costs less than a single 1-carat stone of similar quality.

Color is graded by letter, starting with D for rare, colorless diamonds. E and F are considered excellent, but G or H diamonds will look just as good to the naked eye. Farther down the scale, you’ll notice differences. “If you put a K color beside a G color, you’ll notice more yellow in the K,” said Russell Shor, an analyst for the Gemological Institute.

Clarity measures diamond flaws, called inclusions, which might appear as tiny spots, clouds or cavities in the stone. The clarity grade SI stands for “slightly included.” VS is a better grade, “very slightly included.” VVS is even higher, “very, very slightly included.” Most inclusions in the VVS-SI range cannot be seen by the untrained eye “unless someone tells you where it is,” Shor said.

Cut measures workmanship, rather than a diamond’s inherent qualities. The way a stone is cut enhances sparkle and luminosity and can hide flaws. The best cut rating, ideal, is rare. About a third of diamonds are rated fair, good or very good.

The Formula

What should you look for in each of the C’s?

“The one thing you should not trade off on is the quality of the cut,” said Shor. “Even a nice color stone, if not well-cut, will be dull and lifeless. But if it’s a middle color — like K — and it’s got a real excellent cut, it will pop and flash with all the sparkle that diamonds are famous for.”

After choosing the cut, “balance the color, clarity and carat weight based on your personal preference to find the best diamond for you and your budget,” said Amanda Gizzi, of the Jewelers of America.

For example, for $2,000, you might pick a 1-carat, K-color stone with a slight inclusion, or a half-carat, G-color, with a very slight inclusion. An L or M-colored diamond at that price “will get you a 2-carat honker, but you’ll definitely notice the yellow and you’ll see some inclusions,” said Shor.

Consumers pay $3,500 on average for engagement rings, says the Jewelers of America.

It’s easy to compare options online. Many sites list the four C’s for each ring they sell. Brick-and-mortar stores should be able to provide grading reports.

Shape and style

Engagement rings traditionally feature gold bands with a center diamond, though some have smaller diamonds on either side. Melissa Colgan of Martha Stewart Weddings, says the engagement ring that Prince William gave to Kate Middleton, a large sapphire surrounded by diamonds, has increased interest in rings with other gemstones.

Diamonds can be cut into many shapes. Round, the most common, offers “the biggest bang for your buck because the difference between the raw and cut diamond is smaller,” Colgan said. But she said unusual shapes with retro looks and names like marquise, Asscher and pear are having a resurgence, partly because celebrities are wearing them.

Whether a shape is flattering depends on your fingers. “If you have long thin fingers, you can wear something like Asscher or princess that is more square-cut,” Colgan said.

“If you have shorter fingers or muscular hands, marquise or oval will elongate your fingers.”

Where to buy

Many major brands, including Macy’s, Kay, Zales, Tiffany and even Costco, sell diamonds both online and in stores.

Some retailers sell online only. Gemvara.com’s site is fun for customizing designs.

Blue Nile has sold engagement rings to 325,000 couples over the Internet, including one for $1.5 million.

Many retail stores offer 30-day returns with no penalty. That’s important for surprise proposals in case the bride-to-be says no, or if she says yes but wants a different ring.

These days, though, couples often shop together for a ring.

And most diamond rings are bought in person, according to Jewelers of America, citing the 2011 Wedding Report. Most people want to see, touch and try before buying.