Gold Purity Explained: 9k, 14k, 18k, 22k, 24k

The Karat System Explained

The karat system measures gold purity in 24 parts. 24k is 99.9% pure gold. Because pure gold is too soft for durable jewellery, it is alloyed with other metals. 22k is 91.6% gold, 18k is 75%, 14k is 58.5%, 9k is 37.5%. The higher the karat, the richer the colour and the greater the metal value — but also the softer the piece.

Fineness Table

24k = 999 fineness. 22k = 916. 18k = 750. 14k = 585. 9k = 375. These numbers appear on the hallmark and are the same across the UK, EU, and internationally recognised jurisdictions.

Colour Varieties

Yellow gold is alloyed with silver and copper and gives the traditional warm tone. White gold is alloyed with palladium or nickel and plated with rhodium for a bright silver appearance; the plating wears and needs renewal every few years. Rose gold uses a higher proportion of copper for its pink tone.

Which Karat for Which Purpose

For pure investment: 22k or 24k bars and coins. For fine daily jewellery: 18k, the standard for luxury makers. For active wear where durability matters most: 14k or 9k. For watches: always 18k — the industry standard for gold cases.

Resale Reality

9k jewellery is valued at 37.5% of spot gold as a floor; 18k at 75%. Signed pieces from Cartier, Tiffany or Van Cleef & Arpels sell above that floor — sometimes well above. Unsigned pieces trade close to metal content. If you want pure metal exposure, bullion from a dealer like SilverGoldBull is more efficient than jewellery.

What the Alloy Metals Actually Do

Pure gold is too soft for most jewellery — it deforms under ordinary handling and will not hold a stone securely. Everything below 24k is gold mixed with other metals, and which metals are used determines both the colour and the behaviour.

Copper adds hardness and warmth. Increasing copper moves the alloy toward rose and red gold, and copper-heavy alloys are noticeably harder than the same karat with silver instead.

Silver lightens the colour toward a greenish yellow and adds less hardness than copper.

Zinc is used to control melting behaviour and colour in some alloys.

Nickel whitens strongly and hardens considerably. It is also the common cause of jewellery contact allergy, and its use is regulated in some jurisdictions.

Palladium whitens without the allergy problem and is more expensive, which is why palladium white gold costs more than nickel white gold at the same karat.

The practical consequences are worth holding onto. Two rings both stamped 18k can differ measurably in hardness depending on their alloy. A rose gold ring is generally harder than a yellow one of the same karat. And white gold's colour comes partly from alloy and mostly from rhodium plating, which is a wear layer that needs periodic renewal — as our care guide explains.

Choosing a Karat by What the Piece Has to Survive

The right karat is a function of use, not of status, and matching them saves both money and disappointment.

Everyday rings take more abuse than any other jewellery: constant contact with hard surfaces, pressure from grip, and impacts. 14k is the sensible default; 9k is harder still. 22k on a hand worn daily will visibly deform within a few years, and 24k faster.

Chains worn under clothing experience friction rather than impact. Higher karats survive this reasonably, but the clasp and the jump ring should be well made regardless — that is where chains actually fail.

Earrings take almost no mechanical stress and are a good place for higher karat and richer colour.

Bracelets and bangles knock against desks and door frames constantly. Harder alloys, and thicker sections, last longer.

Settings holding stones need to hold their shape. A claw in very soft gold bends, and a bent claw loses a stone. This is one of the strongest arguments for 18k or below in any piece with stones you would be upset to lose.

Pieces worn occasionally can be anything. If a piece comes out four times a year, softness is not a practical problem and the colour of high-karat gold is the point.

And for anything intended as a store of metal value rather than as jewellery, the answer is bullion rather than any karat — the retail markup on jewellery dwarfs the difference between karats, as our spread guide sets out.

How Purity Interacts With Price

The relationship between karat and price is less direct than people assume, and understanding it prevents a common error.

The metal content scales with fineness: 18k contains twice the gold of 9k by weight. But the metal is often the smaller part of a retail jewellery price. Design, brand, labour, stones and retail margin make up the rest, and none of them scales with karat.

So a heavily worked 9k piece can cost more than a plain 18k one, and correctly so — you are buying the work. Conversely, a plain 22k chain sold near metal value in a market that prices making charges separately can be extraordinary value by comparison with a Western retail 18k chain, which is one of the structural differences our buying abroad guide covers.

On resale, only the metal content has a floor. A buyer pricing scrap pays for fine gold weight and nothing else, which is why our selling guide recommends calculating that number yourself before accepting any offer.

The practical takeaway: judge jewellery on whether you want the object, and judge metal value separately and arithmetically. Conflating the two is how people conclude that a purchase was an investment and discover otherwise at the point of sale.

Purity Marks You Will Meet, and the Ones That Mislead

Marks indicating fineness come in two conventions and several traps.

Millesimal figures state parts per thousand: 999, 916, 750, 585, 375. Karat figures state parts in 24: 24K, 22K, 18K, 14K, 9K. Both describe the same thing and many pieces carry both.

The traps are in the marks that look similar and mean something else entirely:

GP, GEP, HGE indicate electroplating. GF and fractions like `1/20 14K GF` indicate gold-filled. RGP is rolled gold plate. Vermeil is gold over sterling silver, and a `925` mark on a gold-coloured piece is the signature. Our gold-filled guide covers what each construction is worth.

Assay tolerance matters too. Alloys are made to a target fineness with a permitted tolerance, and jurisdictions differ in how much negative tolerance they allow. In systems with compulsory independent assay, a hallmarked piece has been tested against the standard. In systems relying on self-marking, it has not, which is where undercarating has historically appeared — our international hallmarks guide sets out which countries are which.

And the mark tells you nothing about how much gold is present, only its fineness. A hollow 18k bangle and a solid one carry the same stamp and contain very different quantities of metal.

Frequently Asked Questions