The average cost of a diamond ring can vary greatly depending upon the particulars of the diamond itself. Many factors can effect the cost of a diamond. The cut or shape of the diamond is one of these factors. For example round diamonds are usually more affordable than a square or heart shaped diamond. Karat size greatly affects the average cost of a diamond ring. And the bigger it gets the faster the price rises. You can get 1/4 karat for hundreds while a full karat will cost thousands. Clarity, and color also effect the diamond cost. If you are looking for a one karat diamond of good quality and clarity, plan on spending around $5,000 or more.