Weight versus size of a diamond
Larger diamonds are rarer and hence they fetch a higher price. The larger the diamond, the more expensive it is.
There are other considerations, too. Raw, unprocessed, unfinished stones – many carats in weight – are perceived less valuable owing to their inherent flaws, inclusions and some other imperfections.
Large stones may well be inferior, low-grade diamonds with several hidden flaws, an apparent lack of sparkle, and similar such devaluing characteristics. Also, the setting and cut can make a diamond look smaller (or larger) than its actual weight.
A one carat diamond can cost almost double the price of a half-carat diamond (assuming the colour, cut and clarity remain constant). To illustrate further, a one carat diamond solitaire engagement ring will be more expensive than a ring carrying the same quality multiple diamonds, even though they total one carat or perhaps more.
Apart from considering both the size and carat (weight) specifications, a diamond’s choice should be determined by a wearer’s hand and fingers constitution. A large stone may look out of place on a petite hand whereas a tiny stone may look insignificant or almost invisible on a larger finger. The stone’s shape should ideally be proportioned to the fingers on which it will rest.