Understanding Karats and Carats
Two of the most misunderstood and confused terms in the precious metals and jewelry industry are karat and carat. They sound nearly identical, they are spelled similarly, and customers use them interchangeably. You need to know exactly what each one means and be able to explain the difference clearly and confidently.
The Karat System: How Gold Purity Works
Karat is a measurement of gold purity. It uses a fraction system where 24 is always the denominator. So when you see a karat number, you are looking at how many parts out of 24 parts are pure gold.
For example, 14 karat gold means 14 parts out of 24 total parts are gold, and the remaining 10 parts are other metals such as copper, silver, zinc, or nickel. Those other metals are added intentionally to improve hardness, durability, and workability, since pure gold is too soft for most jewelry applications.
The formula: Divide the karat number by 24 to get the percentage of pure gold. So for 18K, 18 is divided by 24 which equals 0.75, meaning 18K gold is 75% pure gold.
Karat Markings and European Fineness Equivalents
In the United States, gold purity is expressed in karats. In Europe and most of the rest of the world, purity is expressed as a three digit fineness number representing parts per thousand. You will encounter both systems regularly, especially when buying estate jewelry or working with international clients.
| Karat (USA) | Pure Gold Content | Percentage | European Fineness Mark |
|---|---|---|---|
| 24K | 24 out of 24 parts | 99.9% pure | .999 or .9999 |
| 23K | 23 out of 24 parts | 95.8% pure | 965 |
| 22K | 22 out of 24 parts | 91.7% pure | .916 or 917 |
| 21K | 21 out of 24 parts | 87.5% pure | 875 |
| 18K | 18 out of 24 parts | 75.0% pure | .750 or 750 |
| 14K | 14 out of 24 parts | 58.3% pure | .585 or 585 |
| 10K | 10 out of 24 parts | 41.7% pure | .417 or 417 |
| 9K | 9 out of 24 parts | 37.5% pure | .375 or 375 |
| 8K | 8 out of 24 parts | 33.3% pure | .333 or 333 |
U.S. Legal Minimum — The FTC Rule: Under Federal Trade Commission guidelines, 10K is the minimum karat that can legally be sold and stamped as gold jewelry in the United States. Any item below 10K purity cannot be marked, advertised, or sold as gold in the U.S. market. Selling or stamping sub-10K material as gold is a deceptive trade practice under FTC rules governing the jewelry industry.
In Europe and the UK the threshold is lower. 9K gold is widely accepted, legally stamped, and sold throughout those markets. You will encounter 9K pieces regularly when buying estate jewelry, particularly from European collections or from customers who purchased jewelry abroad. The 375 fineness stamp is the giveaway.
Underkarat Gold: The FTC recognizes that goldsmiths are artists, not aerospace engineers, and allows a small tolerance below the stated karat. A jeweler stamping a piece 14K is not expected to hit 58.333% gold to the decimal. However, that tolerance is not a license to deceive. Cheap wholesale manufacturers routinely push to the edge of the allowance, producing “14K” jewelry that tests closer to 13K. High-end jewelers go the opposite direction, using alloys that meet or exceed the stated karat.
Karat Plumb (KP): When a jeweler wants to guarantee their gold fully meets the stated karat fraction without any tolerance shortfall, they mark it KP. A stamp reading 14KP means the piece is guaranteed to be at least 14 karat, not a fraction below. KP is a mark of quality and integrity. When you see it, you are looking at a piece made by someone who holds themselves to a higher standard than the law requires.
Carat: A Completely Different Measurement
Carat, spelled with a C, has nothing to do with gold purity. It is a unit of weight used exclusively for gemstones, most commonly diamonds. One carat equals exactly 200 milligrams, or 0.2 grams.
When a customer says their diamond ring is a “two carat diamond,” they are telling you the diamond weighs 0.4 grams. Carat weight is one of the primary factors that determines a diamond’s value, alongside cut, color, and clarity.
Karat (K or KT)
Measures gold purity. Based on a fraction out of 24. Applies only to gold alloys.
Carat (ct)
Measures gemstone weight. One carat equals 0.2 grams. Applies to diamonds and other gemstones.
Why This Matters on the Floor
Clients will hand you a piece of jewelry along with a write up that says “it is 18 carat gold” or “it is a one karat diamond.” They will mix up the terms constantly. Your job is to understand what they actually mean, clarify when necessary, and never make them feel embarrassed for not knowing the difference.
A professional corrects with confidence and without condescension. And a professional knows exactly when to write “ct” and when to write “kt.” That distinction matters on paperwork, in appraisals, and in any written communication with clients or employers. Getting it wrong signals inexperience. Getting it right signals that you belong in this business.