Karats (or Carats) are used to measure the purity of gold alloyed with other metals. 24 karat (24K) is pure gold with no other metals. Lower karats gold contain less gold; 18 karat (18K) gold contains 75 per cent gold and 25 per cent other metals, often copper or silver. 

Fineness is another way of expressing the precious metal content of gold jewellery and represents the purity in parts per thousand, for example 999 gold and 916 gold.  

In summary, the higher the karat, the purer the gold. Typically, the higher the karat, the more valuable the gold would be, and the richer the colour will look. It is also important to note that due to the natural characteristics of gold itself, the purer the gold, the softer and more malleable it is. This is the reason why lower karat gold such as 22K or 18K gold may be more durable and practical for people who wears the jewellery every day or lead more active lifestyles.  

Common Gold Karats and Fineness 

24K/999  

Metals containing 99.9% of gold. In theory, 24 carat should be 1000 (24/24 = 1.00). However, in practice, there is likely to be a very slight impurity in any gold, and it can only be refined to a fineness level of 999.9 parts per thousand. This is stated as 999.9. 23K/999 gold are the purest type of gold available and are very popularly used as a symbol of wealth and prosperity. This gold type is commonly used to make gold bars, gold Pixius, etc.  

22K/916  

Metals containing 91.6% of gold. This is one of the most popular gold purity sought by people, regardless of culture or occasion. These gold jewellery pieces are a great balance between value and durability.   

18K/750  

Metals containing 75% of gold. This is another very popular option for gold buying customers. 18K/750 gold comes in a paler yellow that is not as rich as 24K/999 and 22K/916, and they can even come in white gold form as well. The colour of the gold would depend on the alloy mixed with gold. For white gold, a Rhodium plating is common to give the jewellery a brighter, cleaner look.  

14K/585  

Strictly speaking, 14K gold should be 583 (14/24 = .5833), but most manufacturers have adopted the European practice of making 14K gold slightly over 14K. Thus, the fineness mark is 585 in most 14K gold jewellery. 14K/585 may be a very pale yellow or white gold colour.