Just like all gemstones, the weight of a diamond is measured in carats. A carat is a metric unit of measurement that is exactly 1/5 of a gram (0.20). That means there are five carats to a gram. Carats are divided into 100 points (like pennies in a dollar).
While some people think bigger is better, no one can argue the fact that bigger means more expensive if all other factors are equal.
The carat weight of a diamond can be closely related to a stone’s rarity. It is much harder to find a rough diamond that will yield a one-carat stone than it is to find two rough diamonds that will each produce a 0.50-carat diamond. Because of this, a one-carat diamond is substantially more expensive per carat then a half-carat stone. Therefore, as the diamond increases in size, the per carat price increases exponentially instead of proportionally.