Gold Purity Explained

A practical guide to carats, percentages and millesimal fineness marks.

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Carat Is a Ratio

Gold carat measures how many parts out of 24 are gold. Dividing the carat by 24 gives the approximate pure-gold proportion. For example, 18 ÷ 24 = 75%, so 18ct gold is approximately 75% gold.

Common Jewellery Purities

Approximate pure-gold percentages. Actual recognised hallmark standards depend on jurisdiction and the item.

Gold Factory sells jewellery across a range of purities, including 9ct, 14ct, 18ct, 21ct and 22ct, subject to product availability. 24ct is most commonly encountered in high-purity bullion and some jewellery traditions.

Carat vs Carat Weight

Gold carat (ct) describes purity. Diamond carat (ct) describes weight. They use the same abbreviation but measure completely different things.

Why Alloy Content Matters

The non-gold portion of an alloy influences colour, hardness and manufacturing behaviour. Two pieces can have the same gold carat but differ in colour and physical characteristics because their alloy recipes are different.

Frequently Asked Questions

Approximately 91.6% gold.

75% gold.

It indicates a gold fineness of 375 parts per thousand, commonly associated with 9ct gold.

21ct jewellery is common in some international markets, but UK hallmark standards should be checked on the actual item rather than assuming an 875 UK hallmark.

Ask Gold Factory

If you would like help applying any of this information to a real piece of jewellery, visit us at 294 Farnham Road, Slough, SL1 4XL, call 01753 536800 or contact us through www.goldfactory.co.uk. Jewellery can vary, so our team can explain the options for the actual item you are considering.

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Monday to Saturday: 11:00 am to 6:30 pm. Sunday closed.

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