The ounces of gold present in 1-karat gold depends directly on the weight of the sample because a karat is a ratio, not a measurement of weight. A piece of 18-karat gold contains 18 parts gold and 6 parts other metals, as described by Zales.
In the United States, metal cannot be called gold unless the metal is at least 10 karat. An ounce of 10-karat gold contains 10 parts of gold out of 24 parts, or 41.7 percent gold. Therefore, an ounce of 10-karat gold contains 0.417 ounces of gold, as stated by About.com. Metals most commonly mixed with gold for jewelry include copper, zinc and silver. The ratio of other metals determines the color of the gold, as noted by the World Gold Council.