The number stamped inside a ring almost always tells you the purity of the metal, expressed as parts per thousand. A ring stamped “750,” for example, is 75% pure gold. A ring stamped “925” is 92.5% pure silver (sterling silver). Some rings also carry a second number indicating the carat weight of a gemstone, and occasionally you’ll find a manufacturer’s code. Here’s how to tell them apart.
Gold Purity Numbers
Gold rings use a system called millesimal fineness, which states how many parts out of 1,000 are pure gold. The most common stamps you’ll encounter are:
- 375 = 9 karat, 37.5% pure gold
- 585 = 14 karat, 58.5% pure gold
- 750 = 18 karat, 75% pure gold
- 916 = 22 karat, 91.6% pure gold
- 999 = 24 karat, 99.9% pure gold (rare in rings because it’s too soft for daily wear)
Some rings use the karat system instead, stamped as “10K,” “14K,” “18K,” or “24K.” These convey the same information. A 14K stamp and a 585 stamp mean exactly the same thing. The three-digit number is more common in European jewelry, while the karat system dominates in the United States.
The remaining percentage that isn’t gold is made up of other metals like copper, silver, or zinc, added to make the ring harder and more durable. A 375 ring contains more of these alloy metals than a 750 ring, which is why higher-karat gold feels softer and has a deeper yellow color.
Silver Purity Numbers
Silver rings follow the same parts-per-thousand system:
- 800 = continental silver, 80% pure
- 925 = sterling silver, 92.5% pure
- 950 = Britannia silver, 95% pure
- 999 = fine silver, 99.9% pure
Sterling silver (925) is by far the most common. The remaining 7.5% is typically copper, which adds strength. If you have a gold-colored ring stamped “925,” you’re likely looking at vermeil, which is sterling silver coated with a layer of gold. To qualify as vermeil, the base must be at least .925 silver and the gold plating must be at least 10 karats.
Platinum and Palladium Numbers
Platinum rings carry stamps of 850, 900, 950, or 999. A “950” stamp means the ring is 95% pure platinum, which is the most common grade for platinum jewelry. The 850 and 900 grades were added as recognized standards in 1999. Like gold and silver, these numbers represent parts per thousand.
Palladium, a lighter and less expensive member of the platinum family, uses the same system. Common palladium stamps are 500, 950, and 999. Platinum stamps are sometimes enclosed in a five-sided shape, while palladium may appear in a different outline depending on the country, helping jewelers quickly identify which metal they’re looking at.
Carat Weight Stamps for Gemstones
Not every number inside a ring refers to metal purity. If you see a decimal number like “.50” or “1.01,” that’s the carat weight of the diamond or gemstone. A stamp of .50 means a half-carat stone. A stamp of 1.01 means a diamond weighing one carat and one point.
Some rings have two carat weight stamps. This typically means one number represents the center stone and the other represents the combined weight of the smaller side stones. You might also see abbreviations after the number: “cw” for carat weight, “ct” for carat, or “tdw” for total diamond weight. A stamp reading “.75tdw” means all the diamonds in the ring weigh three-quarters of a carat combined, not that a single stone is that size.
The abbreviation “SOL” before a carat weight indicates the stone is a solitaire diamond.
Gold-Plated and Gold-Filled Marks
If the number inside your ring is followed by certain letters, the piece may not be solid gold. Here’s what those letters mean:
- GP = gold plated (a thin layer of gold over a base metal)
- GE or HGE = gold electroplated or heavy gold electroplate (a slightly thicker plated layer, but still not solid)
- GF = gold filled (a much thicker layer of gold bonded to a base metal, more valuable than plating)
- RGP = rolled gold plate
A stamp like “18K GP” means the ring is plated with 18-karat gold but the core is a different, less valuable metal. Gold-filled pieces sometimes include a fraction: “1/10 10K GF” means 10% of the item’s total weight is 10-karat gold. These pieces have more gold content than plated items and hold up better over time, but they’re still not solid gold.
Maker’s Marks and Other Codes
You may also find letters, logos, or longer numbers that don’t match any purity standard. These are typically maker’s marks, which identify the manufacturer or brand. They can be initials, a small symbol, or a short alphanumeric code. A longer number that doesn’t correspond to a standard fineness (like a five- or six-digit number) could be a model number, serial number, or patent number.
The easiest way to tell a purity stamp from everything else: purity numbers are almost always three digits (375, 585, 750, 916, 925, 950, 999) or follow the karat format (10K, 14K, 18K, 24K). Anything that doesn’t fit those patterns is likely identifying the jeweler or the specific piece rather than telling you what the ring is made of.
How to Read Multiple Stamps Together
A ring can carry several stamps at once. A typical example might read “750 .45ct” on the inside of the band. That tells you the ring is 18-karat gold with a diamond weighing just under half a carat. Another ring might show “925” alongside a small logo, meaning it’s sterling silver made by a specific manufacturer.
If the stamps are worn or hard to read, a jeweler can test the metal with acid or an electronic tester and use a loupe to identify faded marks. Older rings, especially antiques, sometimes carry hallmarks from specific assay offices that verified the metal’s purity at the time of manufacture. These vary by country and era, but the core numbering system for metal purity has remained consistent for decades across international standards.