Carat or Karat? A Little History of Gold, Gemstones & Purity

If you've ever wondered why a diamond is measured in carats, while a gold ring might be described as 14 karat, you're certainly not alone.

The two words are remarkably similar—and they have a shared history. Both ultimately trace their origins to the ancient world and, surprisingly, to the humble carob seed.

Today, carat generally refers to the weight of gemstones, while karat is used to describe the purity of gold in countries such as the United States and Canada. But the story behind these little words is much older, and considerably more interesting, than their modern definitions suggest.

From Carob Seeds to Carats

The word carat comes ultimately from the Greek keration, meaning "carob seed." Carob seeds were historically believed to have a remarkably consistent weight, and for centuries they were associated with the weighing of small, valuable objects such as gemstones.

The idea that carob seeds were perfectly uniform in weight is actually a myth. Like all natural seeds, they vary. Nevertheless, the association endured, and the word passed through Arabic and Italian before eventually becoming the English carat.

For much of history, however, there was no universal standard for exactly how much a carat weighed.

That changed in the twentieth century.

In 1907, the Fourth General Conference on Weights and Measures adopted the metric carat as exactly 200 milligrams, or 0.2 grams. This is the carat we use today when weighing diamonds and other gemstones.

So when a jeweler tells you a sapphire weighs 2 carats, they are telling you that the stone weighs 0.4 grams.

It doesn't tell you the stone's dimensions, however. Two gemstones can weigh exactly the same number of carats and look quite different depending on their shape, density, and proportions.

So What Is a Karat?

This is where things become slightly confusing.

Although carat and karat share a linguistic history, karat is a measure of gold purity rather than weight.

Gold is naturally extremely soft, so most jewelry is made from an alloy of gold mixed with other metals such as silver, copper, palladium, or zinc.

The karat system expresses how much of that alloy is pure gold out of a total of 24 parts.

Think of 24 karats as the whole pie.

• 24K = 24 parts gold out of 24 = essentially pure gold
• 22K = 22 parts gold out of 24 = about 91.7% gold
• 18K = 18 parts gold out of 24 = 75% gold
• 14K = 14 parts gold out of 24 = 58.5% gold
• 10K = 10 parts gold out of 24 = 41.7% gold
• 9K = 9 parts gold out of 24 = 37.5% gold

This is why you may see an antique ring described as 18 karat gold even though it contains other metals. The "18" doesn't refer to weight. It refers to the proportion of the metal that is gold.

Why 24?

This is one of those charming historical details for which there isn't a single universally accepted explanation.

The use of 24 as the whole probably relates to ancient systems of counting and weighing, where 12 and 24 were particularly useful divisions because they can be divided evenly into halves, thirds, quarters, sixths, and eighths.

The system eventually became established in European goldsmithing as a convenient way of expressing the fineness of gold.

Interestingly, the 24-part system is not actually universal today.

Karat in America, Carat in Britain

Here's where jewelry terminology gets especially interesting.

In the United States, gold purity is generally expressed in karats, abbreviated K:

18K gold
14K gold
10K gold

In the United Kingdom and many other countries, gold purity is traditionally described in terms of carat:

18 carat gold
14 carat gold
9 carat gold

So a British jeweler might describe a ring as 18ct gold, while an American jeweler would call exactly the same alloy 18K gold.

They mean the same thing.

The spelling is different, but the underlying 24-part system is the same.

This is particularly useful to remember when shopping for antique jewelry in Britain or Europe. A British auction listing describing an antique ring as 18ct gold is not talking about the weight of the ring or the gemstones. It is telling you that the gold is 18 parts pure gold out of 24.

The European Alternative: Fineness

There is another system you will encounter frequently when buying European jewelry: fineness.

Instead of expressing gold as a fraction of 24, fineness expresses it as parts per thousand.

So:

Karat	Gold Content	Fineness
24K	~99.9%	999
22K	~91.7%	917
18K	75%	750
14K	~58.5%	585
10K	~41.7%	417
9K	37.5%	375

This is why you may encounter jewelry stamped 750, 585, or 375 rather than 18K, 14K, or 9K.

A 750 mark, for example, means that the alloy contains 750 parts pure gold per 1,000 parts metal—or 75% gold.

In other words:

750 = 18K = 18ct

Different notation, same purity.

What About 9 Carat Gold?

This is an especially interesting distinction for American jewelry buyers.

9 carat gold is common in Britain, but it is not legally considered gold in the United States under the same standard used for karat-marked gold. At 37.5% pure gold, 9ct is considerably lower in gold content than 14K.

Historically, 9ct gold became popular in Britain partly because it offered a more affordable alternative to higher-purity gold while still being legally recognized as gold under British standards.

Today, you'll frequently encounter 9ct gold in British antique and vintage jewelry.

For collectors of British jewelry, this means a piece stamped 375 is telling you something important: it is 9ct gold.

And What About 20K?

If you collect antique jewelry, you may occasionally encounter purities that aren't as familiar as 14K or 18K.

20K gold is approximately 83.3% pure gold and may be encountered in certain historical or international jewelry.

You may also encounter 22K gold, particularly in jewelry from South Asia, the Middle East, and other regions where high-purity gold jewelry has long been popular.

The higher the karat, the greater the proportion of pure gold—but that doesn't necessarily mean the jewelry is "better."

It means the alloy contains more gold.

Does Higher Karat Mean Better Gold?

Not necessarily.

It depends on what you want from the jewelry.

24K gold is exceptionally pure but also very soft. It can scratch and deform more easily, which makes it less practical for many types of everyday jewelry.

18K gold offers a beautiful balance between purity, durability, and the rich color associated with high-karat gold. It has long been favored for fine jewelry.

14K gold is more durable and contains a greater proportion of alloy metals, making it particularly practical for everyday wear.

9K gold is even more durable and affordable, although its gold content is substantially lower.

There are also differences in color. The exact shade of yellow, rose, or white gold depends not only on the karat but on which metals are used in the alloy.

An 18K yellow gold alloy and an 18K rose gold alloy contain the same proportion of gold, but the remaining 25% can be composed differently, producing very different colors.

A Useful Trick for Remembering

If you find yourself getting confused between the two terms, remember:

Carat = gemstones
Karat = gold purity

At least in American English.

In Britain and many other parts of the world, however, carat is also used for gold purity.

So:

2 carats = a gemstone weighing 0.4 grams

while:

18K gold = 75% pure gold

and:

18ct gold = also 75% pure gold.

One word measures weight.

The other measures purity.

And, in a delightful bit of linguistic history, both words ultimately lead us back to the tiny carob seed.

Why This Matters When Buying Antique Jewelry

Understanding these markings can be particularly useful when buying antique and vintage jewelry.

A ring stamped 18K, 18ct, or 750 is telling you something about its gold content—but the stamp itself doesn't necessarily tell you when the piece was made, where it was made, or whether every component is original.

Antique jewelry can also contain old alloys, unusual regional standards, or hallmarks that require a little detective work.

That is part of the pleasure of collecting.

A tiny number stamped inside a ring can open the door to a much larger story: where the jewel was made, who might have worn it, what goldsmithing traditions influenced it, and how its materials were valued in its own time.

For those of us who love old jewelry, these little marks are more than numbers.

They're clues.

And sometimes, the smallest clue leads to the most fascinating story.