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Carats vs karats. 1 carat diamonds vs 24 carat gold. It seems like the jewellery industry is deliberately trying to be as confusing as possible! We'll set you straight with this short article that explains what is meant by carats in the context of gold, the history of the term, and the most common gold caratages.
What does carat mean when talking about gold?
Gold caratage refers to the purity of gold expressed as a proportion of 24 parts. It is the standard used to measure the quality or "fineness" of gold, with 24 carat gold being pure gold (known in the trade as "fine gold").
Since pure gold is too soft to make jewellery, it is alloyed (mixed) with other metals to make it harder (and also to change its colour, for example, to create white gold and rose gold).
The higher the gold caratage, the higher the purity and the greater the value. However, when judging the value of a piece of jewellery, it is also essential to consider the amount of gold and the quality of the design and the craftsmanship. At Ingle & Rhode, our gold engagement rings and wedding rings are crafted in 18ct gold as standard, though we can also make your engagement ring in other finenesses on request.
The history of the term ‘carat’
The word "carat" is derived from an Ancient Greek word (keration) via Arabic (qīrāṭ) and Medieval French and Italian for the carob seed. This is because carob seeds were used as a standard for measuring the weight of precious gems and metals.
Carats are still used as a measure of weight for diamonds and gemstones, and in 1907 the International Committee of Weights and Measures set the metric carat at 200mg.
Before this, however, as the practice of alloying gold with other metals became more widespread, the term "carat" came to be used as a measure of the purity of the gold rather than its weight.
In the UK, we spell it "carat" (and abbreviate it to "ct"), whether referring to the weight of diamonds and gemstones (e.g. 1ct diamond) or the purity of gold (e.g. 24ct gold). In the US, the word is spelt "carat" only when referring to diamond and gemstone weight, but when referring to gold purity, the word is spelt "karat" (and abbreviated to "kt").
The connection between weight and purity is that when alloying gold, we measure the amount of gold and the other metals in terms of their weight rather than their volume. So, 18ct gold contains 18 parts gold and six parts of other metals (alloys) by weight.
The most common gold caratages
| Gold Carats | Gold Content (by weight) | Usage |
|---|---|---|
| 24ct gold | 24 out of 24 parts gold (100% pure) | Used in gold bullion. Too soft for use in jewellery |
| 22ct gold | 22 out of 24 parts gold (91.7% pure) | Popular in India for fine jewellery |
| 18ct gold | 18 out of 24 parts gold (75% pure) | The standard for fine jewellery in the UK |
| 14ct gold | 14 out of 24 parts gold (58.3% pure) | The standard for fine jewellery in the US |
| 10ct gold | 10 out of 24 parts gold (41.7% pure) | The standard for costume jewellery in the US |
| 9ct gold | 9 out of 24 parts gold (37.5% pure) | The standard for costume jewellery in the UK |
FAQs
Do carat and karat mean the same thing?
They can do, but not necessarily! The word carat is used internationally as a unit of weight for diamonds and gemstones (e.g. a 1 carat diamond). In the UK, the word carat is also used as a measure for the purity or fineness of gold (e.g. 18 carat gold). However, in the US, the word is spelt karat when used in this way (e.g. 14 karat gold).
What is the highest carat of gold?
100% pure gold is also known as 24 carat or 24 karat gold. It isn't possible to go any higher than 100% pure, so 24 is the highest carat or karat you can go!
Is 9ct gold harder than 18ct gold?
Yes, 9ct gold scores higher on the Mohs scale of hardness than 18ct gold. However, this does not necessarily mean that it is more hard-wearing in the long term. 9ct gold is more brittle than 18ct gold and less resistant to tarnish and corrosion than the higher-carat alloy.
What is the hallmark for 9ct gold?
The UK hallmark for 9ct gold is 375, which reflects the fact that it is 375 parts out of a thousand or 37.5% pure.
What is the UK hallmark for 18ct gold?
The UK hallmark for 18ct gold is 750, which reflects the fact that it is 750 parts out of a thousand or 75% pure.
Summary
Gold carats or karats refer to the purity of gold, measured in terms of the proportion of gold by weight out of 24 parts. 24 carat gold is there for pure gold, whereas 18ct gold contains 18 out of 24 parts by weight gold.
The word carat originates from the use of carob seeds as a way to measure the weight of precious metals and gems before the metric carat was set at 200mg in 1907 by the International Committee of Weights and Measures.
The most popular gold caratages or finenesses in the UK are 18ct gold and 9ct gold, whereas in the US 14ct and 10ct are more common, and in India, 22ct gold is a popular standard.
