Gold Purity Explained: 999, 999.9 and Karats

6 min read · Updated 16 August 2026

Every bullion bar carries a purity stamp — usually 999 or 999.9. Both describe how much of the bar is gold and how much is everything else. Here is what the numbers mean and where the distinction actually matters.

Fineness: parts per thousand

Bullion purity is expressed as fineness, meaning parts of gold per thousand parts of metal. 999 fine gold is 99.9% gold — three nines. 999.9 is 99.99% gold — four nines, sometimes written as .9999. The remainder in either case is trace elements left over from refining, not deliberately added alloy.

Does 999.9 buy you more than 999?

Materially, barely. The difference between the two is nine hundredths of one percent — on a 100 g bar, under a tenth of a gram of gold. It does not meaningfully change what the bar is worth, and both trade on the same spot price.

What the stamp does tell you is something about the refiner. Consistently hitting four nines requires tighter process control, and refiners that do it tend to be the ones with full LBMA accreditation and the strongest resale recognition. Buy for the refiner's reputation and the bar's liquidity — the fineness stamp is a signal of those things more than a value difference in itself.

Karats, and why 24K jewellery is not a bar

Karat is the older scale, expressing gold content in twenty-fourths: 24K is pure gold, 18K is eighteen parts gold to six parts other metal, and so on. Jewellery is alloyed deliberately, because pure gold is too soft to hold a setting or resist scratching — 916 (22K) and 750 (18K) are the common jewellery standards.

That alloying is why jewellery and bullion are not interchangeable as investments. A 22K chain contains real gold, but you also paid for craftsmanship, design and retail markup that the metal itself will not return when you sell. Jewellery also generally falls outside IPM status, so GST applies. If your objective is to own gold rather than wear it, a bar is the more direct instrument.

What to actually check on a bar

• The refiner's name, and whether it is LBMA-accredited.
• Stated weight, and fineness of at least 995 for IPM eligibility.
• A serial number on bars where the refiner issues one.
• An intact assay card or seal, where the bar was sold with one.
• That the dealer will test the bar in front of you.

Purity stamps can be faked, which is exactly why the stamp is the starting point rather than the proof. Precision weighing, ultrasound and XRF together confirm that what is stamped on the outside matches what is inside.