Carat weight (ctw) is a measure of a diamond's weight. One carat is equal to 200 milligrams.
The formula to convert carat weight to millimeters for a round brilliant cut diamond is:
\[ \text{Millimeters} = \left( \frac{\text{Carat Weight}}{0.0061} \right)^{\frac{1}{3}} \]
Consider a diamond with a carat weight of 0.1 ctw:
Using the formula:
\[ \text{Millimeters} = \left( \frac{0.1}{0.0061} \right)^{\frac{1}{3}} \approx 3.02 \text{ mm} \]
This means the diameter of the diamond is approximately 3.02 mm.