9ct vs 18ct Gold: What Do 375 and 750 Mean?
At a glance
9ct gold contains 37.5% gold, while 18ct gold contains 75% gold. The numbers 375 and 750 express those proportions in parts per thousand. Choosing between them starts with the actual piece, your budget and how you intend to wear it.
What is the difference between carat and fineness?
Carat describes gold purity on a 24-part scale. Nine parts out of 24 equal 37.5%, and eighteen parts equal 75%. A fineness number expresses the same composition out of 1,000. Neither number describes a gemstone's size or weight.
Does a 375 stamp prove a piece is genuine?
A 375 mark describes a gold fineness. It should not be confused with a complete UK hallmark, which also includes a sponsor's mark and an assay-office mark. The UK system is a useful reference for interpreting marks, not a statement that Australian jewellery must carry a UK hallmark. If authenticity is uncertain, ask a qualified jeweller to examine the item rather than relying on a photograph of a number.
How should you compare two pieces?
Put their specifications side by side: metal purity, dimensions, weight if supplied, construction, stone details and price. Compare equivalent designs before deciding what represents value to you. A delicate chain and a substantial ring answer different needs, even when both are described as 9ct.
What should you ask before buying?
Ask whether the stated purity applies to the whole piece or a particular component, whether the construction is hollow or solid, and which care instructions apply. Save the written product description with your receipt. For a gift, establish the recipient's preferred metal colour and whether the item needs a specific size before selecting the carat.
Is 18ct always the better choice?
There is no single best choice for every buyer. 18ct gold has a higher gold content, but your decision should also account for design, fit and cost. Do not treat purity alone as a promise about the lifetime of a finished piece.
9ct and 18ct gold compared
| Detail | 9ct gold | 18ct gold |
|---|---|---|
| Gold content | 37.5% | 75% |
| Fineness number | 375 | 750 |
| Construction | Check whether the piece is hollow or solid | Check whether the piece is hollow or solid |
| Buying checks | Size, weight, finish, fittings and price | Size, weight, finish, fittings and price |
Does “solid gold” mean a chain has solid links?
Ask which meaning is intended. Metal composition and physical construction are separate specifications. A chain can be made from a gold alloy while having hollow links. When comparing two listings, request both the gold purity and construction rather than relying on a single phrase.
Where should I start shopping?
For necklaces, compare 9ct gold chains with 18ct gold chains, matching the length and style as closely as possible. For earrings, explore sleepers or hoops and check the metal selected on the product page. For a ring, compare signet designs by face dimensions and fit as well as purity.
Sources and further reading
Material facts and care guidance: Birmingham Assay Office: Gold assay and hallmarking. Checked 8 November 2026. Practical shopping checklists are Kaedesigns editorial guidance; they do not certify the condition or treatment of a particular item.