What is the weight of a diamond carat?


The Bottom Line

When looking at diamond carat weights, it is important to look at the large diamond in the store that is not an AGS Ideal cut. This is because the AGS Ideal cut diamonds are 2mm bigger in diameter than any other gem or diamond you might find in the store.

In order to find the carat weight of any diamond bracelet, first, use the chart below to identify the diameter of the stone in millimetres (mm). Next, look up the stone’s actual weight in carats (ct). Finally, divide the weight of the stone by 200 to determine its ‘points’ measurement in milligrams (mg). For example, a diamond measuring 7mm has a carat weight of 7/200 = 0.35ct. The diamond weighs 3.5ct/200 = 0.175mg per ‘point.’

The weight of a diamond in carats can be used to accurately determine the value of an individual diamond and to compare the value of diamonds of varying sizes to one another. For example, if two diamonds have identical carat weights, but one weighs 0.20 carats and the other weighs 0.40 carats, then the 0.20-carat diamond is worth half as much as the 0.40-carat diamond in per-carat terms.

What is the weight of a diamond carat?

A Brief History of the GIA Diamond Grading System

Before GIA developed its Four Cs system in 1953, diamond grading was quite subjective. The diamond industry was plagued by deceitful practices and unscrupulous marketing tactics, which could mislead buyers about stone quality. (Remember, diamonds are actually made up of carbon). The American Gem Society (AGS) had been around since 1908, but it also didn’t have an official grading system. In 1948, brothers Charles and Sidney Woolf realized they needed to do something to stop these misrepresentations, so they founded Gemological Institute America (GIA). Originally established as a trade school for jewellers and gemologists, GIA launched its grading service in 1953.

What is a Carat?

A carat, abbreviated ct, measures a diamond’s weight in comparison to one-fifth of a gram. In order to determine a diamond’s carat value, divide its weight by 5. The resulting number equals that of a carat. For example, if a diamond weighs 1.01 grams, it has a carat value of 2ct. The various fractional values for carats are: 0.2 ct = 1⁄2 ct = 1⁄4 ct = 1⁄8 ct = 4μ (4 micrograms).

Diamond Price Per Carat

However, prices increase exponentially rather than incrementally. Certain carat values called markers to have less markup and therefore, appear to be better value. This does not mean that they are actually any more valuable, but it gives you an indication of how prices will increase with respect to carat size: Diamonds Carat Weight Marker Points Total Carat Value 1 0.10 ct. 0.1 10 $100 2 0.25 ct. 0.2 25 $200 3 0.35 ct.. 0.3 35 $300 4 0.40 ct.


Diamond carat weights are traditionally broken down into magic sizes – half a carat, three-quarter carat, and carat. Half-carat diamonds are exactly 50 points. Three-quarter-carats are 75 points, and one full carat is 100 points. This system makes it easy to visualize diamond weights. For example, if someone asked you about a two-millimetre diamond, you would know that two millimetres were equal to 50 points – close enough to half a carat for most people! Similarly, if someone described their best engagement rings size as 7 three quarter (what we call 73⁄4) they would probably be talking about 75 points – close enough to three-quarters of a carat for most people!

Diamond Carat Size and Rarity

The size and rarity of the diamond both play a role in the carat. The larger the diamond, the more per carat it costs. In other words, you’ll be paying more for any given diamond if it’s larger, regardless of other factors such as colour or clarity. For example, if you’re looking at two diamonds that weigh 1 carat each and are equally clear, you’ll most likely pay more for the bigger one. Again, it all comes down to supply and demand: there are simply fewer larger diamonds on the market than smaller ones. At least, there’s less demand for them; therefore we see lower prices per carat in larger stones compared to their smaller counterparts.

Eye-Cleanliness is Paramount

With diamond carat size, it’s important to consider eye-cleanliness. One thing to look for is inclusions that are visible to a trained gemologist. A higher-grade diamond, such as an IF clarity grade, will have fewer inclusions than a lower-grade stone. This doesn’t mean a lower-grade diamond is inherently inferior; these stones may still be quite beautiful and valuable and one of these can be your best bet if you’re on a budget. Generally speaking, though, diamonds with fewer inclusions sell for less per carat than diamonds with more inclusions.