Understanding of the Term CARAT for Birthstones

Role of Term CARAT in Birthstones

Whenever you go for the study about the jewelry or make plan to purchase jewelry, you have to come across with the term CARAT. According the perception of people this term is a sign of quality but there are some individuals that have knowledge what does it mean?

It will be not beneficial for you to make a decision on the vague understanding of CARAT. Having the true knowledge about the terminologies of jewelry can be profitable for you while purchasing jewelry items.

Difference between CARAT and KARAT

The unit of measurement of all types of gemstones or birthstone is CARAT that has abbreviation “ct” .  One CARAT is equal to 0.2 grams or 1/5 grams. The term CARAT is genuinely related to gemstones not to the gold.

On other hand to measure the purity of the gold the term KARAT is used. Pure gold is 24 KARAT but often the jewelers add some other metals in the gold to make jewelry items hard and consistent. As diamond is Aries Birthstone and ideal demand must have 1 carat weight and 6.5 mm size.

In pronunciation CARAT and KARAT are the same but in application these are two different terms but applicable in the same niche.

Historical Background of CARAT

In 1907 Fourth General Conference of Weight and Measurement is held in which it was decided that the unit for measurement of birthstones and pearls is CARAT. Later on this term got the standard of measurement of birthstones across the world. The sub units of CARAT are the term POINTS that is 100 points of two milligram each. CARAT is term that is very useful in estimation of cost of the birthstones. For diamond four key factors are helpful for its price estimation that are CARAT, CUT, CALARITY and COLOR.

Formulas for Calculation of CARAT Weight

As we have already explained that

1 CARAT = 200 mg or 0.2 g

There is memorable fact that is different from the size and volume of a birthstone.

It is experimental fact that all minerals own diverse densities and same is in case of birthstone as they are minerals. Therefor one CARAT of diamond will not be the same as for another birthstone in weight.

Calculating Diamond Weight in CARAT

If you are going to calculate the CARATS of diamond, just weigh the stone and convert it into grams. Then divide the number 0.2 to have the desired weight of the diamond.

For instance, if you have piece of diamond that weighs 0.1 grams, then divide the number by 0.2. Your answer will be 0.5. This calculation proves that the stone weighs half CARAT.

How to Calculate the Diamond CARAT Weight by Measurement?

Conversion of grams and milligrams into CARAT is very simple but what happens if scale is unavailable? If you have knowledge of key dimensions of a diamond, you can estimate CARAT weight of diamond. For round shape diamond, you can use the formula below

Weight of Diamond in CARAT = (Diameters) 2 X Depth of Diamond X 0.006

  • Note that in above formula use the units of weight in millimeters.
  • The diameter of the round diamond is line that starts from one girdle, passes from the center of the diamond and touches the other girdle of the diamond. Here girdle is the outer edge of the diamond.
  • The depth of the diamond is the height of the diamond that is from top edge to the lower edge of the stone.
  • The same formula is applicable for the oval shape diamond
  • For example we have a round stone that have dimensions below
  • Girdle diameter = 6 mm
  • Depth of diamond = 3 mm

Now according to the above formula estimated weight of Diamond in CARAT

  • = 6 mm X 6 mm X 3 mm x 0.006
  • =0.7 mm3 approximately

As we have seen practically that diamond is embedded in the jewelery items in more than one shapes so the formula for other shapes like Square and Rectangular Cut is

Estimated weight in CARAT = Length x Width x Depth x Coefficient

The above formula is applicable for various cuts like Emerald Cut, Princess Cut and Radiant Cut

For measurement of dimensions, you should abide by the following rules

  • Length and width of is measurement along the outer edge of the stone that is girdle
  • The depth of the stone is measured in the same way as it was measured for the round shaped diamond that is distance from the top edge of the stone to the bottom edge of the stone. The value of the co-efficient is dependent on the length-to-width ratio of the stone.

The above mentioned formulas give us the estimated value of the weight of the stone in CART but for the accurate weight use Scale


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