Gold purity is the single most important property of any gold you buy – it determines what the metal actually is, how it is used, and what it is worth. Yet the terms can be confusing: karat, fineness, 999.9, hallmarks. This guide explains gold purity in plain language – how the karat and fineness systems work, what 22K, 23K and 24K really mean, how hallmarks fit in, and how purity is verified so you never have to take it on trust.
It is written from the perspective of a licensed exporter that supplies and tests gold from the DRC and Uganda. To go deeper on verification, pair this with our guide on how to verify 999.9 gold from an assay report.
The two ways gold purity is measured: karat and fineness
Gold purity is expressed two ways, and they describe the same thing:
- Karat (K) – parts of pure gold out of 24. Pure gold is 24 karat; lower karats contain proportionally more alloy metals.
- Fineness – parts of pure gold per 1,000. So 999.9 fineness means 99.99% pure gold.
To convert, divide the karat by 24 and multiply by 1,000. For example, 22K = 22 ÷ 24 × 1,000 ≈ 916 fineness.
Gold purity conversion chart
| Karat | Fineness | Approx. % pure gold | Typical use |
|---|---|---|---|
| 24K | 999.9 | 99.99% | Investment bars & coins |
| 23K | ~958 | ~95.8% | Bars & high-purity trade |
| 22K | ~916 | ~91.6% | Bars & durable jewellery |
| 21K | ~875 | ~87.5% | Jewellery (some markets) |
| 18K | 750 | 75% | Jewellery |
What 999.9 / 24K gold means
24 karat – 999.9 fineness – is the highest practical purity, 99.99% pure gold. It is the standard for investment bars and coins because its consistency makes it easy to value and resell. Pure gold is also relatively soft, which is why some applications (especially jewellery) deliberately use lower karats alloyed with other metals for durability.
22K and 23K gold
22K (~916 fineness) is about 91.6% gold, widely traded and also favoured where a slightly more durable metal is wanted. 23K (~958 fineness) sits between 22K and pure gold – a high-purity option common in some bullion markets. CRM offers testing purchases in 23K or 24K and bulk orders of 5 kg and above. Confirm the product, batch-specific purity, assay, documentation and delivery terms in the FCO and SPA. Testing purchases from 100 g to 4 kg are available in 23K or 24K. Prices, payment and delivery terms are confirmed separately before ordering. The bulk deposit schedule does not automatically apply to testing purchases.
Hallmarks, stamps and what they mean
A hallmark or stamp is a mark indicating a piece’s claimed purity (and sometimes the producer). On jewellery and many minted products, hallmarks are common. On investment bars, practices vary: some carry stamps and serial numbers, while others – for security reasons – are not stamped and instead rely on an assay report and a serial-numbered bar list to evidence purity and identity.
The key point for buyers: a stamp is a claim, not proof. Purity is proven by assay, not by a marking. Whether a bar is stamped or not, insist on an assay report and verify the three-way match between the bar, the bar list and the report.
How gold purity is verified
You cannot judge purity by eye or weight alone. Purity is established by assay: non-destructive XRF for fast screening, and fire assay (or refinery acceptance testing) for the definitive result. A reputable supplier provides an assay report stating the fineness and supports independent verification before settlement – see our Lab Testing service and the guide on reading an assay report.
Why purity matters to buyers
Purity determines how gold is valued, how easily it resells, and what it can be used for. Higher-purity 24K is the benchmark for investment and reserve holding; 22K and 23K serve trade and durability needs. Whatever you buy, the assay-confirmed purity – not the declared figure or the stamp – is what counts, which is why documentation and settlement on refinery assay protect you. For choosing between forms, see our guide on dore vs refined vs 999.9 bars.
How Congo Rare Minerals documents purity
Congo Rare Minerals (Reg. No. CRM offers testing purchases in 23K or 24K and bulk orders of 5 kg and above. Confirm the product, batch-specific purity, assay, documentation and delivery terms in the FCO and SPA. Testing purchases from 100 g to 4 kg are available in 23K or 24K. Prices, payment and delivery terms are confirmed separately before ordering. The bulk deposit schedule does not automatically apply to testing purchases. Independent or refinery verification is supported before settlement, and settlement is based on final assay – so you pay on confirmed purity, not a claim. Review our operations on the About page.
Frequently asked questions
What is the difference between karat and fineness?
Karat measures parts of pure gold out of 24 (24K is pure), while fineness measures parts per 1,000 (999.9 is 99.99% pure). They describe the same purity in different units – divide karat by 24 and multiply by 1,000 to convert.
What does 999.9 gold mean?
999.9 fineness means 99.99% pure gold, equivalent to 24 karat – the highest practical purity and the standard for investment bars and coins.
Is 22K or 24K better?
Neither is universally better. 24K is purest and the investment benchmark; 22K (~91.6%) is more durable and widely traded. The right choice depends on whether you prioritise maximum purity or durability and use.
Do all gold bars have a hallmark or stamp?
No. Some bars are stamped and serial-numbered; others are not stamped for security reasons and rely on an assay report and serial-numbered bar list. Either way, purity is proven by assay, not by a stamp.
How is gold purity verified?
By assay – XRF for fast screening and fire assay (or refinery acceptance testing) for the definitive result. Always request an assay report and verify before settlement.
What purity does Congo Rare Minerals supply?
Orders of 5 kg and above require a 10% deposit of the agreed purchase value before shipment. The deposit is part of the purchase price and is credited against the final balance. After receipt, CRM arranges export documentation and transportation to the nominated refinery or agreed address. For refinery deliveries, the final balance is due within 24 hours of assay confirmation, based on the agreed price and confirmed weight and purity, less the deposit. Client-address testing, acceptance and payment timing are stated in the FCO and SPA. Ownership transfers after final payment is received.
Buy gold with purity you can verify
CRM offers testing purchases in 23K or 24K and bulk orders of 5 kg and above. Confirm the product, batch-specific purity, assay, documentation and delivery terms in the FCO and SPA. Testing purchases from 100 g to 4 kg are available in 23K or 24K. Prices, payment and delivery terms are confirmed separately before ordering. The bulk deposit schedule does not automatically apply to testing purchases. Contact our team to request a quote and assay documentation.
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