What Is the Carat Weight Calculator?
The carat is the standard unit used to measure the mass of gemstones and diamonds. One metric carat equals exactly 0.2 grams (200 milligrams). This calculator converts quickly in both directions — from grams to carats and from carats back to grams — so you can describe a stone's weight in whichever unit you need.
How to Use It
Choose the direction of conversion (Grams → Carats or Carats → Grams), enter the value you want to convert, and the calculator returns the equivalent weight along with the value in grams and milligrams. It works for any positive number, from tiny melee diamonds to large gemstones.
The Formula Explained
Because one carat is defined as 0.2 grams, the relationship is a simple proportional conversion:
$$\text{carat} = \frac{\text{grams}}{0.2}$$ and $$\text{grams} = \text{carat} \times 0.2$$. Equivalently, \(1\ \text{gram} = 5\ \text{carats}\), and \(1\ \text{carat} = 200\ \text{milligrams}\). The metric carat has been the international standard since the early 20th century, replacing older regional definitions.
Worked Example
Suppose a diamond weighs 0.4 grams. Dividing by 0.2 gives $$0.4 \div 0.2 = 2\ \text{carats}.$$ Going the other way, a 1.5-carat stone weighs $$1.5 \times 0.2 = 0.3\ \text{grams},$$ or 300 milligrams.
FAQ
Is a carat the same as a karat? No. A carat (ct) measures gemstone weight, while a karat (k) measures gold purity. They sound alike but are unrelated.
How many milligrams in a carat? Exactly 200 milligrams, since \(1\ \text{carat} = 0.2\ \text{grams}\).
Does carat measure size or weight? Carat measures weight, not physical size. Two stones of equal carat weight can look different in size depending on their density and cut.
