Carats and karats are two different things: the former is a unit of weight for diamonds and other gemstones, and the latter is a measure of the fineness or purity of gold. Every carat weighs 0.007 ounces. Each karat equals 1/24 of the total composition of the metal.
Pure gold is 24 karat but every other fineness (i.e. 18-karat or 10-karat gold) is mixed with other metals. At its purest, gold is too malleable for making jewelry.
Other metals that gold is typically mixed with include silver, copper, zinc and nickel. The additional metals give gold the strength it needs to maintain its designated form.
If you’re not sure how many karats your gold jewelry has, take a close look. Almost all pieces of gold are stamped to indicate the purity of the metal.