Updated
18K means 18 karat gold: 18 parts gold in 24, or 75% pure. On its own, the stamp marks solid gold.
18K, 18KT, 18 KARAT, and 750, the European way of writing it.
Fine jewelry and luxury watches, and widely used in Italy, France and Portugal. 18K GP and 18K gold plated are also common marks on low-cost fashion jewelry, so read every letter after the number.
18K on its own means solid gold. The same number followed by letters means a layer of 18K gold over another metal, which holds far less gold:
| Stamp | What it means | Gold, 5 g ring |
|---|---|---|
18K | Solid 18K gold all the way through | 3.75 g $488.96 |
1/20 18K GF | Gold filled: a bonded layer of at least 10K gold, at least 1/20 of the total weight | 0.19 g $24.45 |
1/40 18K RGP | Rolled gold plate: a bonded layer, at least 1/40 of the total weight | 0.09 g $12.22 |
18K HGE | Heavy gold electroplate: at least 2.5 microns of gold | about $2.52 |
18K GEP18K GP | Gold electroplate or gold plate: at least 0.175 microns of gold | about $0.18 |
Pure gold content at today's $130.39 a gram. Plated rows assume a plain ring with about 4 square centimeters of surface at the FTC minimum thickness (16 CFR 23.3).
Melt value = weight in grams × purity × spot price per gram
Spot prices are quoted per troy ounce, and a troy ounce is 31.1035 grams. Gold spot is $4,055.57, so pure gold is $130.39 a gram.
5 grams of 18K gold: 5 × 0.75 × $130.39 = $488.96
Weigh it in grams on a kitchen or jewelry scale. Set stones add weight, so the true figure is a little lower. A buyer pays less than melt to cover refining and profit. Melt value calculator
Photograph it, then take a close-up of the stamp. GemstoneAI uses a legible stamp for the metal and gives a first read on what you have and what it may be worth. Your first scan is free.
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The middle first-read value from GemstoneAI scans of each kind. All jewelry values.
A stamp is a claim, not proof. Fake jewelry is sometimes stamped with real-looking marks. In the US, a purity mark is supposed to sit next to a maker's trademark, so a purity stamp on its own deserves a closer look.
More checks: how to tell if gold is real and the 5-question ring checker.
Yes, when 18K stands alone or beside a maker's mark. 18K GP, 18K GEP, 18K HGE or 18K gold plated means a thin layer of 18K gold over another metal.
Yes. 18K and 750 both mark 18 karat gold, 75% pure.
About $97.79 per gram at melt today.