Carat Weight Calculator

Carat is the standard unit of mass for diamonds and many other gemstones. The modern metric carat is defined exactly as 200 milligrams, or 0.2 gram. That definition gives jewelers, gemologists, laboratories, insurers, and buyers a consistent way to describe small precious stones. This calculator starts with a weight in carats and converts it to grams, milligrams, avoirdupois ounces, and pounds using recognized mass relationships. The conversion to metric units is exact: multiply carats by 0.2 to obtain grams or by 200 to obtain milligrams. Imperial results use one international avoirdupois ounce equal to 28.349523125 grams and one pound equal to 453.59237 grams. Consequently, one carat is approximately 0.00705479 ounce or 0.000440925 pound. Results are displayed with enough decimal places to make small gemstone weights visible without suggesting that an ordinary jewelry scale can measure unlimited precision. Carat weight measures mass, not physical dimensions or visual size. Two gemstones with the same carat weight may have different diameters because density, cut shape, depth, girdle thickness, and proportions differ. A shallow stone can appear larger face-up than a deeper stone of equal mass. Likewise, a sapphire and a diamond with matching dimensions may not have matching carat weights because their material densities differ. This converter does not estimate weight from dimensions; it converts a known measured carat value. Do not confuse gemstone carats with karats, which describe gold purity. A 24-karat gold alloy is nominally pure gold, while a 2-carat diamond has a mass of 0.4 gram. The words sound alike but represent unrelated measurements. Historical carat standards also varied by location before the metric carat was internationally adopted, so old documents may require specialized interpretation. Use the calculator when preparing inventory records, translating a grading report, comparing laboratory measurements, explaining gemstone mass to a customer, or converting specifications for shipping and insurance forms. For a transaction that depends on exact weight, rely on a calibrated gem scale and the value shown on an independent report. Enter that measured value here to obtain clear equivalents in larger mass units while retaining the familiar carat reference used throughout the jewelry trade.