Gold purity when in bar format is expressed in parts per thousand. A bar stamped 999 is 99.90 % pure gold, while 999.9 (also known as “four nines fine”) is 99.99 % pure. In simple terms for every kilogram of 999 gold contains 999g of gold and 1g of trace metals, 999.9 contains 999.9g of gold and only 0.1g of trace metals.
Detailing gold purity in parts per thousand provides more clarity and precision for investment grade gold. Compared to carat system which can be vague on exact gold content, as it divides gold into 24 parts.
Refining tolerance - The London Good-Delivery standard requires a minimum fineness level of 995 ‰ for large wholesale gold bars. This is the minimum requirement, but most retail mints aim for a higher purity level. Getting gold from three nines to four nines means reducing impurities in the gold down to just 0.01%. This small increase in purity requires extra chemical purification steps, tighter quality control and more detailed assaying.
Branding & marketing - Flagship mints (Royal Canadian Mint, PAMP, Perth Mint, Valcambi, etc.) use 999.9 as a selling point, as an example of highest quality and refining processes. The higher stamp signals top tier manufacturing to the consumer even though the actual practical difference in gold content is tiny.
| Bar size | Extra gold in 999.9 vs 999 | Value @ GBP £2,410 / toz* |
|---|---|---|
| 1 oz (31.103 g) | 0.031 g | ≈ GBP £2.40 |
| 100 g | 0.090 g | ≈ GBP £6.97 |
| 1 kg | 0.900 g | ≈ GBP £69.74 |
*Spot price as of 20 May 2025.
The extra decimal of purity adds just £2.40 per troy ounce, based on the spot price above. This small difference is relatively insignificant when the spot price of gold often moves much that much in a single hour.
Gold dealers calculate there bar retail price as the gold spot price plus a percentage premium. Premiums on gold bars cover refining, insurance, fabrication, logistics and a dealer profit margin. Typical premium ranges:
For smaller bars and wafers, the manufacturing cost dwarfs the value of the extra 0.09 % purity; for a kilo bar the premium you pay the dealer (often £600–900) is several times larger than the GBP £69.74 worth of ‘extra’ gold.
Both purity grades 999 and 999.9 are universally accepted by bullion dealers as investment grade gold. When buying gold bars, what really matters is:
A well known 999 grade bar is usually easier to resell than an obscure four-nines bar from an unknown refinery non-LMBA refinery.
| Consideration | 999 | 999.9 |
|---|---|---|
| Gold content | 99.90 % | 99.99 % (0.09 % more) |
| Typical premium | Slightly lower | Slightly higher |
| Availability | Wide (especially kilo bars) | Wide for small/retail bars; some kilobars |
| Resale | Very liquid if LBMA-approved | Equally liquid; marketing edge |
For most investors, the deciding factor on bar choise is total out the door price, not the extra 0.09%. If a 999.9 gold bar happens to be on sale at the same (or lower) premium, grab it. Otherwise, a trusted-brand 999 bar gives identical exposure to the gold price at a marginally cheaper entry point.
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