Gold purity (24K, 22K, 18K, 999, 916) affects price, durability, and investment value. This complete guide explains what the numbers mean and which purity to buy for your goals.
Walk into any jewellery shop or bullion dealer and you'll hear 24K, 22K, 18K, 999, 916, 750 thrown around interchangeably. These numbers all describe the same thing — how pure the gold is — but expressed in two different systems. Once you understand the conversion, you'll never be confused again.
Karats (K) express purity out of 24. Pure gold is 24 karats because 24/24 = 100%.
Fineness expresses purity per thousand. Pure gold is .999 or .9999 because 999 or 999.9 parts per thousand are gold.
The conversion: Fineness = (Karats / 24) × 1000
| Karat | Fineness | Gold % | Common use |
|---|---|---|---|
| 24K | .999 / .9999 | 99.9% | Investment bars, coins |
| 22K | .916 | 91.6% | Indian jewellery, Sovereigns, Eagles |
| 18K | .750 | 75% | Western jewellery, luxury watches |
| 14K | .585 | 58.5% | US jewellery market |
| 9K | .375 | 37.5% | UK budget jewellery |
24-karat gold (fine gold at .999 or .9999) is what serious investors buy. Every major investment product — PAMP Suisse bars, Perth Mint bars, MMTC-PAMP bars, Chinese Panda coins, Canadian Maple Leaf coins — is .9999 (four nines) fine.
The purity matters for several reasons:
The one drawback of pure gold: it's soft. A 24K coin scratches easily and isn't ideal for jewellery that endures daily wear. For investment, this doesn't matter.
22-karat gold (.916) is the traditional jewellery standard in India, the Middle East, and much of Asia, as well as for some iconic investment coins. The 4% alloy (typically copper or silver) makes it significantly harder and more durable for wearable items.
Notable 22K investment products:
When comparing 22K and 24K products by price, you must compare by gold content — not total weight. A 10g 22K bar contains only 9.16g of gold; a 10g 24K bar contains 9.99g. Always check gold content grams, not product weight grams.
18-karat gold (.750) is the standard for fine Western jewellery and luxury watches. At 75% gold, there's significant alloy content — typically copper, silver, or palladium depending on the colour (yellow, rose, or white gold).
For investment purposes, 18K is generally not recommended:
Exception: if you buy jewellery with genuine vintage or designer value (Cartier, Bulgari, Tiffany), the brand premium may exceed the making charges. But this is jewellery collecting, not bullion investing.
Reputable products have clear hallmarks. On gold bars, look for the fineness number (.999, .9999), refiner's mark, weight, and in India, the BIS HUID number. On coins from major mints, the purity is stamped on the coin itself.
Investment bars from accredited refiners (PAMP, Perth Mint, MMTC-PAMP, Valcambi) come with an assay card or certificate. The bar is sealed in a blister pack that, once broken, cannot be resealed — proof that the contents haven't been tampered with. Keep the assay card; it enhances resale value.
If you're buying secondhand or from an unverified source, a reputable dealer or jeweller can test purity with an XRF analyser (non-destructive) or fire assay (destructive, for legal/insurance purposes). Cost is typically $20–$50 for XRF.
When logging a holding in BullionKeeper, the purity field matters for accurate valuation. The app calculates your portfolio value as weight × purity × spot price. A 10g bar at 22K is worth less at spot than a 10g bar at 24K — the tracker handles this automatically when you enter the correct purity.
Enter purity as: 999 or 999.9 for 24K, 916 for 22K, 750 for 18K. The app converts to decimal and applies to your weight correctly.
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