How to Calculate the Amount of Pure Gold in 10K, 14K & 18K Jewelry

Pure 100 percent gold is called 24 karat gold, which is abbreviated 24K. Most jewelry is made with alloys that strengthen the jewelry but reduce the gold content. Before you sell your unwanted or broken jewelry for its gold value, you need to calculate how much pure gold your jewelry contains.

Find the karat markings on your jewelry. These are usually very small and you may need a magnifying glass or jeweler's loupe to find them. Markings are usually found inside the bands of rings, on necklace and bracelet clasps, on the posts of earrings, and on the back side or on the clasp of pins. Be sure to check for gold markings on white metal -- it may be white gold.

Categorize the markings. The markings may be in the form of 10K, 14K, or 18K, which is the way that most jewelry is sold in the U.S. If the jewelry came from the U.K., it may be marked 9K or 12K. Some jewelry may be marked with European markings, which are 417 (or sometimes 415), 585, or 750.

Sort gold items from other types of jewelry. Items that also have the markings GE, HGE, RGP, GF, or 1/10, 1/20, or 1/30 are not solid gold and cannot be sold for gold value. These items are gold plated or gold filled (which is just a heavier layer of plating). An item with just a P after the karat marking, such as 14 KP, is a solid gold alloy. In this case, the P stands for "plumb", which means "exactly". If your gold jewelry is marked 925 or "Sterling", it is actually gold plated Sterling silver jewelry, not solid gold.

Calculate your gold content. For example, 10K gold is 10 parts out of 24 parts pure gold, or 10/24th's. Since 10 divided by 24 gives the fraction 0.417, your jewelry is about 41.7 percent gold. This is where the European markings come from: 417 means 417 out of 1,000 parts of pure gold.

Likewise, 14K gold is 14/24 = .585, which is equal to 585/1000, making the European marking 585, and the pure gold content 58.5 percent.

For 18K gold, the gold content is 18/24 = .750 = 75 percent pure gold, also marked 750.

The same can be calculated for other gold markings: 9K (sometimes marked 375), 20K (833), 21K (875), 22K (917). Some vintage jewelry from the UK may also be marked 8K or 333.