Karat vs. Carat: What's the Difference?

Two words, nearly identical spelling, completely different meanings — karat and carat trip up even people who shop for jewelry regularly. Here's the difference, in plain terms.

Karat: Gold Purity

Karat (spelled with a K) measures how much pure gold is in a piece of jewelry, out of 24 parts. 24K is pure gold. 18K is 18/24, or 75% pure gold. 14K is 58.3% pure gold. 10K is 41.7% pure gold. The remaining percentage in each case is other metals — copper, silver, palladium — alloyed in for strength and durability.

Carat: Gemstone Weight

Carat (spelled with a C) measures the weight of a gemstone — most commonly a diamond, but the term applies to any gem. One carat equals 200 milligrams. It has nothing to do with purity or quality on its own; a 1-carat diamond can range enormously in value depending on its cut, clarity, and color, so carat weight alone doesn't tell you much about a stone's quality.

Why the Confusion Happens

Both words come from the same linguistic root — the carob seed, historically used as a small, consistent unit of weight for trading gold and gemstones. They split into two different measurement systems over time: one for metal purity, one for gem weight. The shared origin is exactly why the spelling still looks so similar today.

A Quick Way to Remember

Karat = gold purity (K). Carat = stone weight (C). If you're reading a number followed by "K" — 10K, 14K, 18K — it's about the gold. If it's followed by "ct" or "carat," it's about the stone.

Want the specifics on gold karats? Read our full 10K vs. 14K vs. 18K guide.