Gold Purity Explained: Karats, Fineness, and Hallmarks
Two gold rings can look identical and still be worth very different amounts. The reason is almost never the design. It is purity: how much of the metal is actually gold and how much is something else. If you have ever squinted at a tiny “750” or “18K” stamped inside a band and wondered what it meant, this guide is for you. It is information, not financial advice.
Purity is the first thing a serious buyer checks, because it drives both the melt value and the price a dealer will pay. Get comfortable with two systems, karats and fineness, and you can decode almost any piece of gold in seconds.
Karats: the traditional scale
The karat system splits gold into 24 parts. Pure gold is 24 karat, meaning 24 out of 24 parts are gold. Every lower number tells you how many of those 24 parts are gold and how many are other metals such as copper, silver, or zinc, which are added to make the metal harder and to shift its color.
The math is simple. Divide the karat number by 24 to get the gold content as a percentage.
| Karat | Gold content | Common use |
|---|---|---|
| 24K | 99.9 percent | Bullion, some Asian jewelry |
| 22K | 91.7 percent | Coins, heirloom jewelry |
| 18K | 75.0 percent | Fine jewelry |
| 14K | 58.3 percent | Everyday jewelry (common in the US) |
| 10K | 41.7 percent | Budget jewelry, minimum legal “gold” in the US |
Pure 24K gold is soft and scratches easily, which is why most jewelry is 14K or 18K. Those alloys trade a little purity for a lot of durability.
Fineness: the modern scale
Fineness measures the same thing on a scale of 1,000. It tells you how many parts out of 1,000 are pure gold. An item marked “750” is 750 parts gold per 1,000, which is exactly 75 percent, the same as 18K. Bullion bars and coins usually carry the fineness mark rather than a karat stamp.
You will see these common fineness marks:
- 999.9 or 9999: often called “four nines,” the standard for investment-grade bullion.
- 999: “three nines,” still bullion grade.
- 916: matches 22K, common on gold coins.
- 750: matches 18K.
- 585: matches 14K.
To convert a karat figure to fineness, divide the karat by 24 and multiply by 1,000. So 14K becomes roughly 583 to 585, depending on rounding.
Reading a hallmark
A hallmark is the set of small stamps on a gold item. Depending on where it was made, it can tell you the purity, the maker, the assay office that tested it, and sometimes the year. The purity mark is the one that matters most for value. Look for a number like 750 or 585, or a karat stamp like 18K or 14K.
Be careful with a few things. A stamp reading “18KGP,” “GP,” “GF,” or “RGP” does not mean solid gold. “GP” means gold plated and “GF” means gold filled, which is a thin layer of gold over a base metal. These carry only a fraction of the gold value of a solid piece. When in doubt, a reputable dealer or assay office can test the metal directly rather than trusting the stamp alone.
Why purity drives price
Bullion pricing starts from pure gold, then scales to the actual gold content of a piece. A one-ounce coin that is 22K contains slightly less than a full ounce of gold, so its metal value reflects that. Jewelry is more complicated because you also pay for craftsmanship, brand, and retail markup, which is why jewelry rarely trades close to its melt value.
With spot gold trading near $4,066 per ounce in late July 2026, according to USAGOLD, the purity gap between 14K and 18K on the same weight of metal is large enough to matter. That is exactly why buyers verify purity before agreeing on a price, and why understanding hard assets is part of a broader picture that firms like Atlas Treasury frame within a diversified allocation.
FAQ
Is higher karat always better? Not for every use. Higher karat means more gold, but softer metal. For jewelry you wear daily, 14K or 18K often makes more sense than 24K.
Does the stamp guarantee the purity? No. Stamps can be worn, faked, or misapplied. For anything of significant value, an independent test is the reliable check.
What is the minimum to be called gold in the US? Legally, 10K (41.7 percent) is the minimum that can be marketed as gold in the United States.
Key takeaway
Karat and fineness are two ways of measuring the same thing: how much pure gold an item contains. Learn to read the number stamped on the metal, watch for plating marks like GP and GF, and you will know what you are buying before money changes hands.
goldgold puritykaratsfinenesshallmarksprecious metals education