The number of carats in gold is a measurement of how much of the alloy (out of 24 parts) is formed of pure gold when we talk about carats. In 9ct gold, for example, 9 pieces out of 24 are pure gold. The remaining 15 components are made of various metals to increase the piece's strength. These include silver, copper, zinc, aluminum, and other materials. One carat is equal to 200 milligrams or 0.2 grams. There are 12 inches in a foot, so 1 ounce (28 grams) is equivalent to about 730 stones (7.3 grams). One ton weighs 2,204.5 pounds, so one stone is equivalent to 28 grams or 0.71 ounce. There are 31.1 grains in a scruple. One hundred scruples make a pound and 454.10 grams. It is also possible to measure weight in ounces or grams: one ounce is 30 grams, one stone is 20-24 ounces, or 40-48 grams. Carats are usually quoted per kilo (2.2 pounds), but can be quoted per gram (0.035 oz.). A karat value of 25% indicates that one quarter of the metal is gold; three quarters is 75%. Because nine times 25% equals 21.8%, the correct answer is between 22 and 26.5 carats.