Gold Percentage to Karat Chart: Reverse Lookup

One Multiplication, Both Directions

The karat system is a fraction with 24 on the bottom. That's the whole system. A karat number tells you how many twenty-fourths of the item are gold, so converting in either direction is a single operation:

Percentage to karat: karat = (percentage ÷ 100) × 24. Shortcut: multiply the percentage by 0.24.

Karat to percentage: percentage = (karat ÷ 24) × 100.

Try it. A piece testing at 75.0% gold: 75 × 0.24 = 18. Eighteen karat, exactly. A piece testing at 58.33%: 58.33 × 0.24 = 14.0. Fourteen karat. A piece testing at 91.67%: 91.67 × 0.24 = 22.0. Twenty-two karat.

Millesimal fineness — the three-digit stamps like 750, 585, 375 — is even easier, because it's just the percentage with the decimal moved: fineness = percentage × 10. So 75% is 750, 58.33% is 583 (stamped 585 by American convention, for reasons covered further down), and 37.5% is 375.

The trouble starts when the multiplication produces something that isn't a whole number. Sixty percent × 0.24 = 14.4 karat. There is no 14.4K. No mint strikes it, no manufacturer stamps it, no hallmarking office recognizes it. The arithmetic is perfectly valid and the answer is perfectly useless, which is exactly why a reverse chart needs a fourth column that a normal karat chart doesn't have: what an off-standard number probably means.

The Reverse Table: Percentage In, Karat Out

This gold percentage to karat chart runs from the bottom of the scale to the top. The second column is the raw arithmetic; the third is the nearest karat anyone actually stamps; the fourth is the practical read.

Only seven of those rows — 9K, 10K, 14K, 18K, 21K, 22K, 24K — cover the overwhelming majority of what walks through an American buyer's door. The rest are the interesting cases.

Why Most Percentages Have No Karat at All

The karat scale is not continuous. It has 24 possible integer positions, and commerce uses maybe seven of them with any regularity. That means that of all the purity percentages a tester can physically report — anything from 0.1% to 99.99% — the vast majority correspond to no karat whatsoever.

This trips people up because purity *feels* like a continuous quantity, and physically it is. An alloy can genuinely be 63.2% gold. Nothing in metallurgy forbids it. What forbids it is the market: goldsmiths mix to established recipes because established recipes are what hallmarking offices certify, what refiners quote against, and what buyers recognize. An alloy nobody recognizes is an alloy nobody wants to pay a premium for.

There's also a legal floor. In the United States, the Federal Trade Commission's jewelry guides mean nothing under 10 karat can be described or sold as gold. In the UK the floor is 9K. In Germany it drops to 8K. So the same 35% alloy is legally "gold" in Frankfurt, borderline in London, and simply not gold in Chicago.

The practical consequence for reverse lookup: when your number lands between two standard karats, the correct first assumption is not "this is an unusual alloy." It's "this is one of the two neighboring standards, and something about my measurement or my source is off." Unusual alloys exist. They are far rarer than imprecise tests, and running the piece through a karat gold calculator at both neighboring karats will show you how much the ambiguity is actually costing you.

Sixty Percent Gold: The Most Common Off-Standard Reading

Sixty percent comes up more than any other non-karat number, and there are three ordinary explanations.

It's a rounded 14K. Fourteen karat is 58.33%. Round that in conversation and "about sixty percent" is what a jeweler says. Nine times out of ten this is the answer, particularly in the US market where 14K is the default.

It's surface enrichment on a real 14K piece. Karat gold jewelry is often finished in a process that strips a little copper and silver from the outermost microns, leaving the surface marginally richer in gold than the body. An XRF gun reads the surface. That surface can genuinely test 59–61% on a piece whose bulk is honestly 58.33%. This is why refiners assay a melted, homogenized sample rather than trusting a surface scan.

It's an off-standard trade alloy. Some jewelry made for markets without strict hallmarking is mixed to whatever the workshop found economical. A 60% piece sold as 15K exists. It is uncommon in the US and worth verifying.

Now the money question, since "cost of 1 gram of 60% gold alloy" is a search people actually run. Assume gold at $4,400 per troy ounce. One troy ounce is 31.103 g, so pure gold is $4,400 ÷ 31.103 = $141.46 per gram. A gram of a genuine 60% alloy contains 0.60 g of gold: 0.60 × $141.46 = $84.88 of gold. A gram of 14K contains 0.5833 g: 0.5833 × $141.46 = $82.51.

The gap is $2.37 per gram. Trivial on an earring. On a 30-gram chain it's $71 — and if the "60%" was really a rounded 14K all along, that $71 was never there. This is precisely the kind of small, invisible discrepancy that makes the difference between two quotes on the same item, so it's worth knowing whether your number is measured or estimated.

Eighty, Eighty-Nine, and Other Numbers That Signal a Problem

80%. Multiply by 0.24 and you get 19.2K, which is not a thing. If you're reading 80% off a stamp — an "800" mark — stop and consider silver. The 800 fineness mark is a widespread European silver standard, common on German and Italian flatware, hollowware, and jewelry. Gold-toned 800 silver is an extremely ordinary object. If instead 80% came from a tester on a gold-colored piece, the two live possibilities are a heavily gold-plated base or a machine reading a thick plating layer rather than the core.

89%. That's 21.36K. Twenty-one karat is 87.5% and twenty-two is 91.67%, so 89% sits almost exactly between them, slightly nearer 21K. In practice this is a 21K Gulf-market piece reading a touch high — same surface-enrichment effect described above, plus normal instrument tolerance. Treat it as 21K unless a destructive assay says otherwise, and price it at 21K, because a buyer will.

65%, 70%, 95%. All non-karats (15.6K, 16.8K, 22.8K). Any of these on a mixed scrap lot usually means the lot was averaged: throw four 14K rings and two 18K bands into one pan and the aggregate reads somewhere in the sixties. Sort by stamp before you test, or you'll be quoted at the average and paid at the lowest.

The general rule for reverse lookup: a percentage that doesn't map to a whole karat is data about your measurement, not about your metal. The London Bullion Market Association publishes the good-delivery standards that define what "assayed purity" means at the wholesale level — see the LBMA's standards documentation — and none of that machinery exists for a reason. Purity claims get expensive when they're wrong, and jewelry from unregulated markets frequently is. If a number keeps landing between standards, that's your cue to learn how to tell real gold from fake before you accept anyone's read.

The Karats That Used to Exist

A handful of the odd rows in the table above are real historical standards, and finding one tells you something about where and when a piece was made.

• 8K (333) — legal in Germany, Austria, and parts of Scandinavia. Exactly one-third gold. Reads copper-pink, tarnishes noticeably, and cannot be sold as gold in the US at all.
• 12K (500) — a genuine half-and-half karat that had a real run in American jewelry in the early twentieth century. Today the "12K" you're most likely to encounter is inside a gold-filled mark, where "1/20 12K GF" means a 12K layer amounting to one-twentieth of the item's weight — total gold content around 2%.
• 15K (625) — a British standard abolished in 1932, when the UK consolidated on 9K, 14K, 18K, and 22K. A genuine 15K hallmark dates a piece to before that year, which occasionally makes it worth more intact than melted.
• 20K (833) — appears sporadically in Middle Eastern and East Asian work.
• 23K (958) — turns up in Thai and some Southeast Asian jewelry, sitting just below bullion purity.

Two of these matter commercially. If you have a hallmarked 15K British piece, get it looked at by someone who knows antique jewelry before scrapping it. And if you have anything stamped with a karat number *plus* letters — GF, GP, GEP, RGP, HGE — the karat describes a coating, not the object, and the percentage-to-karat conversion doesn't apply at all. The full stamp vocabulary is decoded on the gold hallmarks page.

Percent, Fineness, Karat: The Three-Column Cheat Sheet

Three notations, one underlying fact. Here they are side by side for the seven standards that cover almost everything:

Values assume $4,400 per troy ounce, or $141.46 per gram of pure gold. Purity percentages are permanent; the dollar column moves daily, with recent prices running near $4,300–$4,500 per troy ounce.

One notation quirk deserves a note, because it generates its own steady stream of confused searches. Fourteen karat is mathematically 583.3 parts per thousand, and older European pieces are stamped 583 accordingly. American manufacturers standardized on 585 — alloying a hair rich so that a stamped piece would never assay *under* its mark. Both stamps mean 14K and both are worth the same money. Similarly, India's BIS system rounds 22K down to 916 while most other markets round to 917. The World Gold Council maintains market and standards references at gold.org if you want to go deeper on how national hallmarking systems diverged.

For a fuller treatment of each standard, including which regions use which and why, the gold purity chart runs the same data forward instead of backward.

When the Percentage Is Describing a Coating

There's one scenario where a gold percentage to karat chart fails completely, and it's worth flagging because the arithmetic gives you a confident, wrong answer.

Gold plating and gold fill are thin layers of real karat gold over a base metal. A gold-filled chain marked "1/20 14K GF" has a genuine 14K skin — 58.33% gold *in that skin* — bonded over brass. Run a surface tester across it and you may well read something in the fifties, because the tester is reading the skin. Convert that to karat and you'll conclude you have a 14K chain. You have a brass chain with a gold coat, worth a small fraction of solid.

Signals that a percentage is describing a coating rather than a body:

1. A letter suffix on the stamp. GF, GP, GEP, RGP, HGE, or a fraction like 1/20 or 1/10 in front of the karat.
2. Wear-through. Check the highest-friction spots — clasp edges, ring shanks, the underside of a bangle. Base metal showing through as a duller, redder, or grayer color is decisive.
3. A magnet reacts. Gold isn't magnetic and neither is brass, but plenty of plated costume jewelry has a steel core that will grab a magnet immediately.
4. The number moves depending on where you test. A solid alloy tests the same everywhere. Plating doesn't.

For anything you plan to sell, the reliable move is a test that reaches past the surface — an acid test on a filed notch, or a density measurement, both covered on the how to tell real gold from fake page. And once you have a purity you trust, how much is a gram of gold worth converts it straight into dollars.

The Matching Exercise, Answered

A steady share of the traffic for this topic is students working through a homework problem that asks them to match each gold karat to its correct gold content percentage. Here's the answer key, plus the reasoning, since the reasoning is the part worth keeping.

Every one of these is karat ÷ 24. Twenty-two divided by twenty-four is 0.9167. Eighteen divided by twenty-four is 0.75. Ten divided by twenty-four is 0.4167. If you memorize nothing else, memorize the divisor: 24. Every other number falls out of it.

The one asterisk is 24K itself. Mathematically 24/24 = 100%, and textbooks usually accept 100%. Commercially, absolute purity doesn't exist — refined bullion is sold as 999 (three nines) or 9999 (four nines) fine, which is 99.9% or 99.99%. That trailing tenth of a percent is why this site uses 99.9% for 24K in every calculation: it's the honest number for physical metal, and on a kilogram bar the difference is a gram of gold you either have or don't. In the classroom, write 100%. At the counter, expect 999.

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