Karat (Gold Fineness)
Also: kt, ct, Karat gold, Gold karat
Karat (abbreviated kt or ct) is the traditional unit of measurement for the gold content of an alloy: 24 karat equals pure gold (999 ‰ fineness, highest traded purity 999.9 ‰).
Karat (abbreviation kt, less commonly ct) is the oldest and, in the jewellery and coin trade, still the most widely used unit for expressing the gold content of an alloy. The scale ranges from 1 kt to 24 kt, where 24 karat means pure gold. It must not be confused with the identically named carat as a unit of weight for diamonds and gemstones, which has an entirely different meaning.
Origin and background
The term derives from the Arabic qīrāṭ and the Greek kerátion (carob seed) – a historical weight standard. In the Middle Ages, the idea of subdividing gold into 24 equal parts became established because the Byzantine gold solidus weighed 24 siliquae. This subdivision has persisted to this day: each karat corresponds to one twenty-fourth of the total weight of the alloy.
Conversion: karat to fineness (per mille)
Fineness indicates how many grams of pure gold are contained in 1,000 grams of the alloy. The conversion is straightforward:
Fineness (‰) = Karat number × (1,000 ÷ 24)
Example 18 kt: 18 × (1,000 ÷ 24) = 750 ‰
Overview of the most common gold alloys
| Karat | Fineness (‰) | Gold content (%) | Typical use |
|---|---|---|---|
| 24 kt | 999 | 99.9 | Bars, coins (fine gold) |
| 22 kt | 916 | 91.6 | Bullion coins (e.g. Krugerrand) |
| 18 kt | 750 | 75.0 | High-quality jewellery, watches |
| 14 kt | 585 | 58.5 | Most widely used jewellery standard in Germany |
| 9 kt | 375 | 37.5 | Standard in the United Kingdom |
| 8 kt | 333 | 33.3 | Legal minimum standard in Germany |
The current gold price for these alloys can be compared directly in the melt value calculator.
Alloying metals and their effect
Pure gold (24 kt) is very soft and of little practical use for most everyday objects. By alloying with other metals, hardness, colour, and workability are selectively adjusted:
- Copper increases hardness and shifts the colour towards red → red gold
- Silver produces a paler yellow gold and increases ductility
- Palladium or nickel yields white gold (often additionally rhodium-plated)
- Silver + copper together are the classic mix for jewellery gold
The lower the karat value, the higher the proportion of these alloying metals.
Hallmarks and stamps
In Germany and the EU, gold articles weighing 0.5 grams or more must be marked with a fineness hallmark. The per mille values (e.g. 585, 750, 999) are commonly used, while the karat designation is more widespread outside Germany – particularly in the USA and the UK. Historical pieces often still bear karat designations as a hallmark punch.
Karat in investment gold
For investment gold in the tax-law sense (VAT exemption under EU Directive 98/80/EC), gold bars must have a fineness of at least 995 ‰ (corresponding to approximately 23.88 kt) and gold coins at least 900 ‰ (corresponding to 21.6 kt). Bullion coins such as the Krugerrand with 916 ‰ (22 kt) meet this requirement. Note: This is not tax or investment advice; please consult a tax adviser for individual questions.
The material value of a gold alloy can be quickly determined: in the gold calculator enter the weight and karat and you will receive the current melt value based on the spot price.
Distinction: carat (diamond) vs. karat (gold)
| Feature | Karat (gold) | Carat (diamond/gemstone) |
|---|---|---|
| Meaning | Degree of purity (proportion) | Weight |
| Scale | 1–24 | from 0.01 ct upward |
| Unit | Dimensionless (ratio) | 1 ct = 0.2 grams |
| Abbreviation | kt (or ct) | ct |
Further background on the carat as a unit of weight can be found in the glossary entry on diamond weights.
In brief
Karat measures the gold content of an alloy on a scale of 1 to 24 – 24 kt means pure gold. For a quick melt value, use the melt value calculator; those wishing to value scrap gold or dental gold are best served by the dental gold calculator.