Which C primarily indicates the size of a diamond?

The correct answer is carat, as it is the unit of measurement used to indicate the weight and size of a diamond. One carat is equivalent to 200 milligrams. When people refer to the size of a diamond, they are typically discussing its weight in carats, as this directly correlates with how large the diamond appears when viewed. Understanding carat weight helps consumers make informed decisions about the size and presence of a diamond in jewelry.

The other characteristics—cut, color, and clarity—do not measure size. Cut refers to the diamond's shape and how well it has been faceted, which affects the stone's brilliance and light performance. Color denotes the presence or absence of color in a diamond, impacting its overall beauty and value. Clarity describes the presence of internal or external flaws, which also play a role in quality and value but have no direct influence on a diamond's physical size. Each of these attributes affects a diamond's appearance and desirability, but carat is the sole metric that specifically quantifies size.