A gold karat chart answers one question: how much of an alloy is pure gold. Karat counts parts of gold out of 24, so 24k is pure gold, 18k is 18/24 or 75%, 14k is about 58.33% and 10k is about 41.67%. Stamps often give the same purity as parts per thousand, which is why a 14k ring may read 585 and an 18k one 750. The formula is karat ÷ 24, and multiplying by 1,000 gives the fineness number.
Pure gold is too soft for most jewelry, so rings and chains are made from alloys. The chart below lists every common grade from 8k to 24k. After it come the stamps and the hardness trade-off behind 10k, 14k and 18k jewelry. Then come the Federal Trade Commission's rules on karat marks and the word "gold," and a method for estimating the pure gold in a piece. No gold prices appear here, because the topic is gold purity.
How the karat system works
Gold karats form a 24-point scale, so the answer to what 14k gold means is simple: 14 of its 24 parts are gold, which makes 14k gold about 58.33% pure. A piece marked 18k has 18 parts gold and 6 parts other metals, usually copper and silver for yellow gold. The Royal Mint's guide to metal fineness describes the same 24-part ratio, with pure gold at 24. Four formulas cover every calculation in this article:
- Purity as a share = karat ÷ 24
- Fineness (parts per thousand) = karat ÷ 24 × 1,000
- Karat = fineness ÷ 1,000 × 24
- Pure gold in grams = weight × karat ÷ 24
Gold fineness is the same measure written out of 1,000. BullionStar's purity guide explains that refiners, mints and assay offices use it, which is why stamps on gold are often numbers such as 999, 750 or 375 and not karats.
Gold karat chart: 8k to 24k
The percentages and exact fineness values below were calculated by script as karat ÷ 24, rounded to two and one decimal places. The last two columns come from BullionStar's purity chart (linked above) and show the usual stamp and where the grade is typically sold. That chart describes the market as a whole and not only the US. Stamps are conventions and do not always equal the exact result of the division, as the notes under the table explain.
| Karat | Pure gold | Exact fineness | Common stamp | Typical use |
|---|---|---|---|---|
| 8k | 33.33% | 333.3 | 333 | Low-cost jewelry, mainly in Germany |
| 9k | 37.50% | 375.0 | 375 | Budget jewelry in the UK and Australia |
| 10k | 41.67% | 416.7 | 417 | Budget jewelry in the US |
| 12k | 50.00% | 500.0 | 500 | Not covered by the sources used |
| 14k | 58.33% | 583.3 | 585 | Everyday jewelry in the US and Europe |
| 18k | 75.00% | 750.0 | 750 | Fine jewelry and luxury watches |
| 21k | 87.50% | 875.0 | 875 | Middle Eastern jewelry |
| 22k | 91.67% | 916.7 | 916 | Bullion coins and Asian jewelry |
| 24k | 100% | 1,000 | 999 or 999.9 | Bars and bullion coins |
Two caveats apply. First, 14k divides out to 583.3, yet the stamp is usually 585. On a 12 g chain the two values give 7.00 g and 7.02 g of pure gold, a difference of 0.02 g, so the choice rarely matters in practice. Second, 24k is not one number. Good Delivery bars between banks are 995, many coins and bars are 999 and some are 999.9, and all of them count as 24k. The chart is a reference summary and not a legal list. The stamp or an assay report is what states the grade of an actual piece.
What a gold stamp means: 417, 585, 750, 916 and 999
A three-digit number such as 585, 750 or 916 is fineness. What does 585 mean on gold? It means 585 parts gold per 1,000, which is 14k. A karat mark such as "14K" gives the same information in a different format. Dividing a three-digit stamp by 10 gives the purity percentage, so 750 is 75%.
A stamp alone is not proof. BullionStar notes that marks can be forged and that GP, GEP, HGE, GF and RGP stand for gold plated, gold electroplated, heavy gold electroplate, gold filled and rolled gold plate. A piece marked "18K GP" has a thin 18k coating over another metal and is not an 18k piece. The FTC's Jewelry Guides add two details about US marks. Under the National Stamping Act, a manufacturer or dealer covered by the Act must also apply its trademark or name to an article bearing a quality mark, as 15 U.S.C. 297 provides. And the Guides tie karat claims to the Act's tolerances, which are three parts per thousand for gold without solder and seven with solder.
Why 24k is soft and most jewelry is 10k to 18k
Pure gold is very soft. In a 1999 Santa Fe Symposium paper, Christopher Corti of the World Gold Council reports a hardness of about HV 20 to 30 for soft, annealed 24k gold of 99.0% to 99.5% purity. A standard yellow 22k gold-copper-silver alloy measures about HV 52 and an 18k yellow alloy about HV 150 in the same annealed state. HV is the Vickers hardness scale, where a higher number means a harder metal.
That is the reason jewelry is made from alloys. Copper, silver, zinc and other metals harden the gold, and the lower the karat, the more of them there is. The trade-off runs the other way for gold content. Retail guides generally rank the three grades the same way in a 10k vs 14k vs 18k gold comparison. Blue Nile's guide calls 10k the hardest common karat, 14k durable enough for everyday wear and 18k softer and more likely to show wear. Because Blue Nile sells jewelry, treat the ranking as a retailer's view. Its direction matches the hardness figures above. The same guide notes that 10k can irritate skin that reacts to alloy metals such as nickel.
What the FTC Guides say about karat marks and the word "gold"
The Guides for the Jewelry, Precious Metals, and Pewter Industries are the FTC's guidance on honest marking. Under 16 CFR 23.0 they are guidance and not law, but the Commission can act under Section 5 of the FTC Act if a claim conflicts with them. The relevant section is 16 CFR 23.3, and its main points are these:
- A product made throughout of a gold alloy may be called "gold" if the correct karat precedes the word and is as conspicuous, as in "14 Karat Gold" or "14K Gold." The karat can also stand alone, as in "14K."
- "Gold" used alone, without a karat, is misleading unless the product is 24-karat fine gold.
- A hollow gold-alloy product should not be called "solid gold."
The 10-karat rule
Many retail pages still say 10k is the legal minimum for "gold" in the US. That matches the threshold in the earlier Guides. When the FTC published the revised Guides in the Federal Register on August 16, 2018, it removed the minimum thresholds for gold and silver alloys. The notice says marketers may now use gold terms for an alloy above or below 10 karats if they add an accurate, equally conspicuous karat designation. Section 23.3 even uses "9 Karat Gold" as a correct example. State laws or other countries' rules may still differ, and this article did not review them. So is 10k real gold? Under the Guides it can be sold as gold with the karat stated. The 10-karat figure remains in the Guides for gold plating and vermeil, but no longer for solid gold.
Gold filled, gold plated and vermeil
These terms describe coatings, and the Guides give each a definition. Sections 23.3 and 23.4 set the following minimums. Every gold term except vermeil must be preceded by an accurate karat designation.
| Term | What the Guides require |
|---|---|
| Gold electroplate or gold plated | Electroplated gold or gold alloy of at least 10k on all significant surfaces, at least 0.175 micron of fine gold in thickness, and reasonable durability |
| Heavy gold electroplate | Same alloy, at least 2.5 microns of fine gold |
| Gold filled | A mechanically bonded layer of at least 10k that makes up at least 1/20 of the total metal weight |
| Rolled gold plate or gold overlay | Same bonded layer, at least 1/40 of the total metal weight, with the fraction stated |
| Vermeil | Sterling silver base coated on all significant surfaces with at least 10k gold, at least 2.5 microns of fine gold, and reasonable durability |
The table summarizes the FTC's examples of acceptable marking and does not cover every claim the Guides address. Gold filled therefore means a mechanically bonded gold-alloy layer that must make up at least 1/20 of the item's metal weight, while electroplating is judged by thickness. That is the practical difference between gold filled and gold plated.
Karat vs carat
Karat measures the purity of gold. Carat measures the weight of gemstones, and a metric carat is 200 milligrams, according to GIA. GIA adds that carat measures weight and not size. The FTC's Guides list both "karat" and "carat" among quality-mark words in section 23.10. The two units can sit in one description. In "an 18k ring with a 0.5-carat diamond," 18k describes the metal and 0.5 carat describes a stone of 100 milligrams.
How to estimate the pure gold in a piece
Multiply the weight by the karat and divide by 24. The calculations below were run by script, and the weights are hypothetical examples.
| Piece | Weight | Karat | Calculation | Pure gold |
|---|---|---|---|---|
| Chain | 12 g | 14k | 12 × 14 ÷ 24 | 7.00 g |
| Ring | 8.4 g | 18k | 8.4 × 18 ÷ 24 | 6.30 g |
| Bracelet | 5 g | 10k | 5 × 10 ÷ 24 | 2.08 g |
| Bracelet | 5 g | 18k | 5 × 18 ÷ 24 | 3.75 g |
Two bracelets of the same weight therefore hold very different amounts of gold, which is what the karat grade shows. The result is the weight of gold in the alloy and not a price. To turn that weight into a currency amount at the current rate, you can use the gold, crypto and exchange calculator, and the weight converter handles grams and ounces. Jewelry prices also include labor and retail margin, which this calculation leaves out.