If you’ve ever shopped for gold jewellery, you will have noticed the carat of gold (or karat gold) listed in the jewellery description.
But what does this term actually mean?
The gold carat of an item of jewellery shows the purity of gold or the parts of pure gold contained within the item as a proportion of the whole.
Gold Carat and Karat
The Gold Carat or Karat of an item mean exactly the same thing. The word “karat”, spelt with a letter “k”, is used within the USA, and “carat”, spelt with a “c”, is used in most other parts of the world outside of America.
Diamond Carats
Many people are understandably confused about the word “carat” in relation to a piece of jewellery. This is because the weight of gemstones, like diamonds, are also measured in carats, but have a slightly different meaning, despite it being spelt in the same way.
The carat of a gemstone signifies the carat weight of the gemstone (thereby indicating its size). If you want to read more about this, see our article on Diamond Grading here.
The Origins of the Carat/Karat Gold
Many hundreds of years ago, when people bartered items and money changed hands, the German coin – the Mark – was a standard of currency used that many other countries and nationalities recognised. These Mark coins weighed exactly 24 “carats”.
The name “carat” stemmed from the carob seed, which was used as a counterweight in weighing gemstones and metals.
This word gold karat, or gold carat, is still used today as a standard, to measure the weight of fine metal within a piece of gold jewellery or coin or the weight of a gemstone.
Gold As A Currency
At some point in history, as trading became more commonplace, they replaced pure gold coins with coins of gold mixed with other metals, like copper or even silver – known as an alloy.
This had a number of advantages. It made the coins stronger. It preserved rare, precious gold. It also decreased the cost of the gold.
The Fineness of Gold
In order to barter or be used as a currency, people needed to know how much a coin was worth so a system was needed to show how much pure gold was contained within a coin. A standard was needed to measure against.
The German Mark, made in pure gold, weighed 24 carats, shown as 24ct (or 24k for 24 karats). It is against this measurement of whole, pure gold that mixtures of metals, pure gold and an alloy, are used to measure the mass of pure gold in an item made containing gold.
24-carat gold (24ct or 24k) as we have said, is quite soft and not as malleable as gold mixed with other alloys. It is also the gold that will carry the most expensive price tag. It’s basically showing that 24 parts gold out of a total of 24 parts is within the item.
22-carat gold (22ct or 22k) is the next highest gold purity content. The metal is made of 22 parts of pure gold and 2 parts of another metal or mixture of metals (an alloy), such as copper.
If a gold coin contains 75% pure gold and 25% alloys, they marked it as being made of 18k, or 18ct, gold. They often make wedding rings of 18-carat gold.
The next level down of gold is 14-carat gold which is 58.5% pure gold and the rest metal alloys.
Then follows 9-carat gold which is 37.5% pure gold and the remaining metal made up of alloys. Whilst this contains less gold, it has the advantages of being more durable and stronger than 18ct, 22ct or 24ct gold. This makes it an excellent gold for everyday jewellery and for items of jewellery with claws that hold precious gemstones. 9-carat gold also costs less than 14ct or 18ct gold.
9-carat gold is also less “yellow” than 18ct gold and many people prefer the softer colour.
| Carat (UK) | Karat (USA) | % Pure Gold | Fraction of 24 | Millesimal Fineness |
| 9 Carat (9ct) | 9 Karat (9k) | 37.5% | 9/24 | 375 |
| 14 Carat (14ct) | 14 Karat (14k) | 58.3% | 14/24 | 583 or 585 |
| 18 Carat (18ct) | 18 Karat (18k) | 75% | 18/24 | 750 |
| 22 Carat (22ct) | 22 Karat (22k) | 91.7% | 22/24 | 916 or 917 |
| 24 Carat (24ct) | 24 Karat (24k) | 99.9% | 24/24 | 999 |
Millesimal Fineness
The Two Ways of Expressing the Fineness of Gold
As well as the fineness of gold, the amount of pure gold in a piece, being noted by using the word carat or karat gold out of a total of 24 units, there is also another way of displaying the fineness of an item of gold.
This is expressed by the unit of pure gold in an item as a part of 1000, written or stamped on the inside of the item of jewellery, as part of the hallmark. It is known as the millesimal fineness.
So, for instance, 18-carat gold contains 75% in weight of pure gold and will be stamped with ‘750’ as part of the hallmark, meaning that there are 750 parts out of 1000 of pure gold within the item.
Another way of saying this is as a percentage out of 1000 – with the decimal point being removed. 22-carat gold is 91.6% or often just stamped as 916 or 917. See the table below for details.
Other Coloured Gold
The purest gold is a rich yellow gold colour. Making a piece of jewellery by mixing pure gold with other metals like copper or silver, also changed its colour. This made it much more versatile.
Despite the highest carat gold being of a richer yellow gold colour, white gold and rose gold can also be made in all the levels of fine gold. Different metals are mixed in the alloys to create the best colour for the item of jewellery. Rose gold often has more copper in the mix. Welsh gold naturally has more copper content in the soil and this gives it a rich, red colour.
For example, in the case of white gold, they will still mix pure gold with other metals alloys, like silver or copper but will use whiter metals to lighten the colour. They will also cover the piece of white gold jewellery in another metal, rhodium, known as rhodium plating, to give it its white appearance. We have talked about this in our blog, ‘What is White Gold’.
To Sum Up …
So, despite the confusing way of measuring the weight of gemstones – and in particular diamonds – as “carats”, the amount of pure gold within a metal alloy is stated in the number of carats or karats up to a level of 24 carats.
We all need to know exactly what we are buying, particularly when it comes to fine jewellery. Gold has a wonderful way of holding its price and goes up in value over time.
Once you know what the carat value of an item of jewellery means, you will know exactly what you are paying for or whether to hold onto a piece in your jewellery collection or not.
