Diamond Carat Weight

The standard unit of weight for diamonds is the carat (abbreviated as ct.) One carat equals 0.200 gram, or 1/5 gram. In common US measurements, that’s 0.007 ounce (7/1000 ounce). To put this into perspective for a customer, you might say it takes about 142 carats of diamonds to equal one ounce.

As precise a unit as the carat is, it’s not precise enough for something as valuable as a diamond. Fractions of a carat can represent hundreds, or even thousands, of dollars. So the carat is subdivided into 100 equal parts called points. One point (abbreviated pt.) equals 0.01 carat, or 1/100 carat. You can help customers understand this by telling them that 100 points add up to one carat, just as 100 pennies add up to one dollar.

Carat weight is usually written in decimal numbers to two places. For example, a diamond that weighs exactly 1 carat is recorded as 1.00 ct. and one that weighs exactly 1/4 carat is recorded as 0.25 ct.

When professionals talk about diamonds weighing more than a carat, they also use decimals. If you’re presenting a diamond that weighs 1.27 carats, you might say “one point two seven carats” or “one point twenty-seven carats.”

The weights of diamonds less than a carat can be stated in decimals or in points. Thus, you could say a 0.27-carat diamond weighs “point 27 carats,” “twenty-seven hundredths of a carat” or “twenty-seven points.”

Some retail firms don’t allow weight to be given in points because they feel it confuses customers. Others allow it provided that you explain the term when you first use it. So know and follow your store’s policy. Then practice until you can state any diamond’s weight clearly.

In addition to decimals, diamond weight can also be expressed in fractions.

“One-quarter carat” is easier for many customers to understand than “point two five-carat” or “twenty-five hundredths of a carat.” It’s also easier to say. In the diamond industry, however, weight fractions are used approximately and they usually apply to ranges of weight. For example, a “quarter-carat” diamond might weigh from 23 to 29 points.

You don’t need to memorize a lengthy list of weight ranges. Just remember that when suppliers or other professionals say “a quarter carat,” they don’t necessarily mean exactly 0.25 carat.

Customers, however, usually do expect fractions to be mathematically exact. To avoid misunderstandings you need to be careful with weight fractions.

If you’re presenting a diamond that weighs 0.32 carat, you could first say “thirty-two points” or “thirty-two hundredths of a carat.”

Next you might explain, “That’s about a third of a carat.” Then you could use the fraction in the rest of your presentation.


Different firms have different policies 

regarding the use of weight fractions. As with points, know your store’s policy and follow it carefully. If you use approximate fractions, practice explaining them.

When diamond professionals communicate with each other, they describe weight in various ways. Different industry segments such as miners, cutters or dealers, use different terms with each other.

These specialized terms can confuse customers so they’re not appropriate for most retail presentations. You should be familiar with those you may encounter in your work, however.



One common trade term for weight is melee (which rhymes with jelly). It refers to polished diamonds that weigh less than 20 points.


Light half

Another example is light half, which refers to diamonds from 45 to 49 points or light caratwhich refers to 0.95 – 0.99 ct. diamonds.


Grain and grainer

Diamond wholesalers sometimes use the terms grain and grainer. One grain equals 0.25 (1/4) carat, and diamond weights may be described in multiples of that.


Thus, you might hear a dealer refer to a diamond that weighs 0.75 (3/4) carats as a “three grainer.” Like weight fractions, grains are usually approximate. A selection of three-grainers might include diamonds that range from 0.70 to 0.83 carat each.

Cutters and wholesalers also describe small diamonds in terms of how many it takes to equal a carat. For example, diamonds weighing 0.125 carat are sometimes called eights. That’s because 8 x 0.125 ct = 1.00 ct. On a parcel of diamonds or an invoice you might see this written as 1/8s. You could find the average carat weight of the diamonds in the parcel by dividing the top number by the bottom number: 1÷8 = 0.125 ct.


Weight and Value

To help customers understand the relationship between carat weight and value, you may have to overcome commodity thinking. Consumers are used to buying products like meat, fruit, and vegetables by weight. Many precious commodities like gold, silver, and platinum are also sold this way. Diamonds are not commodities, however – so you may need to explain that a diamond’s price is determined by more than just weight – that the diamond’s rarity is most significant in determining value.

A 1-ounce bar of gold is no rarer than two ½-ounce bars, so it will cost no more. In contrast, a 1-carat diamond is much rarer than two ½-carat diamonds of comparable quality. So the larger diamond will be more expensive than the two smaller diamonds added together.

Although this is a simple explanation, it’s an important one. The price effects of clarity and color are also based on rarity. If you establish the link between rarity and value with carat weight, you set the stage for other Cs you need to discuss.


Per-carat Pricing

Differences in rarity are reflected in the per-carat prices of diamonds. Per-carat price is the cost for each carat of a diamond’s weight. Most wholesalers quote diamond prices this way. For example, a wholesaler might say he has a 1.25-carat diamond for $3,000 per carat. To find the total cost of the diamond, you multiply the per-carat price by the weight: $3,000/ct x 1.25 ct = $3,750.

Retailers normally state the total cost of a diamond, but per-carat prices can help customers make comparisons. If you say, “This diamond is $2,000 per carat and this one is $3,000 per carat,” the customer immediately understands there are significant differences. Explaining the differences can lead to other value factors and ultimately to a purchase decision.

Total weight is the combined weight of all the diamonds in an item of jewelry.

When you present jewelry set with more than one diamond, you need to make sure the customer understands whether you’re talking about the weights of individual diamonds, or the sum of them all.

You might say something like, “The large diamond in the center weighs fifty-five points. The three smaller diamonds average twenty-four points – or about a quarter carat-apiece. The total weight of all of the diamonds is one point twenty-seven carats.”

Whether you’re stating the weights of individual diamonds or the total weight of all the diamonds, FTC guidelines say your representation must be accurate to the second decimal place (hundredths of a carat). That means the weight is rounded to the nearest point and the precision is within 1/2 point. If you use approximate weight fractions, you must explain the ranges of weight to which they refer.

Source: Diamond Council of America