A 1.25-carat diamond refers to the weight of a diamond, and it is equivalent to 0.25 grams or 125 milligrams. Carat is the unit of weight used for diamonds and other gemstones, with one carat equal to 0.2 grams. The value of a 1.25-carat diamond depends on several factors, including the cut, color, clarity, and certification. Generally, diamonds with a higher cut grade, color grade, and clarity grade are more valuable.