One of the common misconceptions regarding carats is that some think more carat size means more facets. However, you must be aware that a one carat round brilliant will have 58 facets, and if you buy a 5 carats diamond ring with a round brilliant centerpiece, it will still have the same number of facets. The thing that differs here is the appearance and light reflective properties of the stone.
Diamonds above two carats are rare in nature, and hence, the bigger the size of the diamond, rarer it will be. Apparently, as rarity is directly proportional to the price, more carat size always means that the diamond gets more and more expensive.
Yet another factor that affects the price is whether the ring is antique or not. Antique rings consist of huge diamonds that have a high level of cutting precisions, and hence, are more costly than modern pieces.
One more point to note is that diamond sizes after a certain point are priced in half or full carats. For example, a diamond with 4.9 carats will have the same price as that of a diamond with 4.5 carats. After 4.9 carats, the price of the stone may become considerably high.