Pure gold is designated as “24 karat”. This means there are 24 parts gold out of a possible 24 parts (100%). Gold jewelry usually is mixed with other metals, called alloys, which lowers the actual gold content in the piece and makes it harder. You will normally see a marking on the item somewhere which indicates the amount of gold in the piece, such as 10k, 14k or 18k. When you see a piece marked 18k, that means 18 parts out of a possible 24 parts are gold, which is 75%. The European designation for this is 750, meaning 750 parts gold out of 1000 parts possible. Therefore, 25% of the metal in the piece is some other alloy, such as silver, nickel, copper, etc. Likewise, a piece marked 14k is 14 parts gold out of a possible 24 parts, or 58.3% gold. Sometimes it is marked 585, which is 585 parts gold out of 1000 possible parts. But be aware that the markings could be counterfeit. If you are uncertain, there are tests which help determine if a piece of jewelry is real gold or plated.