Gold Karat Converter

Understanding Gold Purity Measurements

Gold purity is expressed using two primary systems: the karat system (common in the United States and most English-speaking countries) and the millesimal fineness system (common in Europe and international trade). Both systems describe the proportion of pure gold in an alloy, but they use different scales.

The Karat System:

The karat system divides gold into 24 parts. Pure gold is 24 karat (24K). The karat number indicates how many of those 24 parts are pure gold, with the remainder being other metals (copper, silver, zinc, nickel, etc.).

Purity percentage = (Karat / 24) × 100 Karat = (Purity percentage / 100) × 24

The Millesimal Fineness System:

Fineness expresses purity in parts per thousand. This system is more precise and is the international standard.

Fineness = (Karat / 24) × 1000 Karat = (Fineness / 1000) × 24

By that arithmetic 24K comes out at 1000, but a bar is stamped 999, or 999.9 for investment grade. That is not an error in either place, and the table below sets out why.

Common Gold Purity Levels:

The two fineness columns are not the same thing, and the gap is where most confusion on this subject lives. “Nominal” is what the karat arithmetic gives you. “Stamped” is the legal alloy standard actually marked on the piece.

Two rows deserve a word. 24K is 1000 by the arithmetic and 999 on the bar, because absolute purity is not achievable in refining; investment gold is stamped 999 or 999.9 and nobody stamps a flat 1000. 14K is stamped 585, which is above its nominal 583.3, because the legal standard for the alloy was set at a round 58.5 percent rather than at exactly fourteen twenty-fourths. The extra tenth of a percent is real gold, deliberately added so the piece cannot fall under standard on assay. Everywhere else the stamp is just the nominal figure rounded to three digits.

International Hallmark Stamps:

Different countries stamp gold with different marks to indicate purity:

• US / Canada: Karat stamp (e.g., 14K, 18K)
• UK: Fineness stamp (e.g., 375, 585, 750)
• Italy / Europe: Fineness stamp (e.g., 750 for 18K)
• India: Hallmark with karat and fineness (e.g., 22K 916)

Gold Alloy Colors:

The metals mixed with gold determine the alloy’s color:

• Yellow gold: Gold + copper + silver (classic warm color)
• White gold: Gold + palladium or nickel + zinc (silvery appearance)
• Rose gold: Gold + higher copper content (pinkish hue)
• Green gold: Gold + higher silver content (subtle green tint)

Practical Examples:

• An 18K gold ring is 75% pure gold and 25% other metals. If gold is $2,000 per troy ounce, the gold content in one troy ounce of 18K alloy is worth $1,500.
• A piece stamped “585” is 14K gold (58.5% pure). A piece stamped “750” is 18K (75% pure).
• US law requires gold to be at least 10K (41.7% pure) to be sold as “gold jewelry.” In the UK, the minimum is 9K (37.5%).

Tips:

• Higher karat gold is softer and more prone to scratching. 14K and 18K are popular for daily-wear jewelry because they balance purity with durability.
• “Gold-filled” (GF) and “gold-plated” (GP) are NOT solid gold. Gold-filled has a thick layer of gold bonded to a base metal, while gold-plated has a very thin gold coating applied by electroplating.
• When buying gold jewelry internationally, look for the fineness stamp rather than karat to avoid confusion between regional standards.
• Pure 24K gold does not tarnish or corrode, but lower karats may show slight discoloration over time due to the alloy metals.