The Meaning of Karat
A karat number indicates the parts of gold contained in a piece of jewelry, out of a maximum of 24.
For example, a 14-karat bracelet has 14 parts pure gold out of 24, and the remaining 10 parts are made up of other metals, usually copper, nickel or zinc.
In the same way, a 22-karat gold chain will contain 22 parts gold and 2 parts other metals.
Converting Karats to Gold Purity Percentages
Converting karats to a percentage of purity is pretty straightforward. You just need to divide the karat number by 24 and then multiply by 100.
For example, to calculate the percentage of gold in an 18-karat ring, you need to divide 18 by 24 and then multiply by 100, yielding 75% gold purity (and implying the presence of 25% other alloys in the ring).
Karat Stamps and Their Meanings
Karats are most often indicated by marking gold jewelry with the karat number, followed by a karat symbol: K, k, Kt, kt, or KT.
For example, the markings “10kt” and “10K” mean the same – the piece contains 10 karats gold.
Instead of karats, sometimes you may see gold purity numbers stamped on jewelry as percentages or thousandths.
For example, a stamp reading “999” (or “.999”) means that the gold is 99.9% pure, which corresponds to 24K.
Sometimes, you will see the letter “P” stamped next to the karat number.
For example, a marking “18KP” (read, “eighteen karats plumb”) means that the gold content of the piece is guaranteed to be at least 18 karats.
If you look at your jewelry and cannot see any karat marks, you can have your piece tested for purity. Many jewelers provide this service – they will take your jewelry and use acid (as in this gold testing kit) to establish its exact karat.
Standard Karat Values
The most popular karat values for gold jewelry are 10K, 14K, 18K, 20K and 22K. (It is rare to see 24K jewelry as pure gold is too soft.)
It is important to remember that jewelry with gold purity of less than 10K is not technically considered gold in the U.S.
Keep in mind that unless your gold jewelry is marked as “plumb” (as in “14KP”), the exact karat may vary slightly from what is stamped on the piece. In the U.S., the allowed variation is +/-0.5 karats, meaning that your 14K gold may actually be 13.5 karats.
What Other Metals Does Gold Jewelry Contain?
Since pure gold is very soft, it is mixed with other metals to create jewelry that is durable. The resulting material is actually a gold alloy.
The metals most often used for this purpose are copper, nickel, zinc, and sometimes, aluminum. The concentration of those additional metals in the alloy can also change the color of the gold jewelry; for example, white gold gets its white color from nickel and zinc.
How High and Low Karats Differ
Generally, the lower the karat and the less gold in your jewelry, the harder and more durable it will be.
The downside to that is that the less gold there is, the less the jewelry will look like… gold.
Also, since gold alloys often contain nickel, if you are allergic to it, the lower the karat, the more likely it is that you will experience skin irritation.
Higher karat jewelry, on the other hand, looks better, but since it contains more gold, it is also likely to scratch more easily.
It seems that 14K and 18K pieces tend to be the most popular since these karat levels offer a good combination of durability, appearance and price while not causing allergic reactions.