Karat (Gold Fineness)
Also: kt, ct, Karat gold, Gold karat
Karat (abbreviated kt or ct) is the traditional unit for the gold content of an alloy: 24 karat corresponds to pure gold (999 per mille fineness, with the highest trade purity being 999.9 per mille).
The karat (abbreviated kt, less often ct) is the oldest unit still in everyday use in the jewellery and coin trade for expressing the gold content of an alloy. The scale runs from 1 kt to 24 kt, with 24 karat meaning pure gold. It should not be confused with the identically named carat as a unit of weight for diamonds and gemstones, which carries an entirely different meaning.
Origin and background
The term derives from the Arabic qirat and the Greek keration (carob-tree seed), a historical weight standard. In the Middle Ages the idea took hold of dividing gold into 24 equal parts, because the Byzantine gold solidus weighed 24 siliquae. That subdivision has survived to this day: each karat equals one twenty-fourth of the alloy's total weight.
Conversion: karat to fineness (per mille)
The fineness states how many grams of pure gold are contained in 1,000 grams of the alloy. The conversion is straightforward:
Fineness (per mille) = Karat number x (1,000 / 24)
Example 18 kt: 18 x (1,000 / 24) = 750 per mille
Overview of the most common gold alloys
| Karat | Fineness (per mille) | Gold content (%) | Typical use |
|---|---|---|---|
| 24 kt | 999 | 99.9 | Bars, coins (fine gold) |
| 22 kt | 916 | 91.6 | Bullion coins (e.g. the Krugerrand) |
| 18 kt | 750 | 75.0 | High-quality jewellery, watches |
| 14 kt | 585 | 58.5 | Widely used jewellery standard |
| 9 kt | 375 | 37.5 | Standard in the UK and Ireland |
| 8 kt | 333 | 33.3 | Lowest legal standard in Germany |
You can compare the current gold price for these alloys directly in the melt value calculator.
Alloying metals and their effect
Pure gold (24 kt) is very soft and poorly suited to most everyday objects. By alloying it with other metals, hardness, colour and workability are deliberately controlled:
- Copper raises hardness and shifts the colour towards red -> red gold
- Silver produces a paler yellow gold and increases ductility
- Palladium or nickel yield white gold (often additionally rhodium-plated)
- Silver plus copper together are the classic mix for jewellery gold
The lower the karat value, the greater the proportion of these alloying metals.
Hallmarks and stamps
In many EU countries, gold articles above a certain weight must carry a fineness hallmark. The per-mille values (for example 585, 750, 999) are common, while the karat statement is more widespread outside continental Europe, especially in the USA and the UK. Historical pieces often still bear karat statements as a hallmark.
Karat in investment gold
For investment gold in the VAT sense, gold bars must have a fineness of at least 995 per mille (roughly 23.88 kt) and gold coins at least 900 per mille (roughly 21.6 kt). Bullion coins such as the Krugerrand at 916 per mille (22 kt) meet this requirement. In Ireland investment gold is exempt from VAT under the VAT Consolidation Act 2010 and EU Directive 2006/112/EC. Note: this is not tax or investment advice; please consult a tax adviser for individual questions.
The material value of a gold alloy is quickly established: in the gold calculator you enter weight and karat and receive the current melt value based on the spot price.
Distinction: karat (diamond) versus karat (gold)
| Feature | Karat (gold) | Carat (diamond/gemstone) |
|---|---|---|
| Meaning | Purity level (proportion) | Weight |
| Scale | 1-24 | from 0.01 ct upwards |
| Unit | dimensionless (ratio) | 1 ct = 0.2 grams |
| Abbreviation | kt (or ct) | ct |
Further background on the carat as a measure of weight can be found in the glossary entry on diamond weights.
Key takeaway
Karat measures the gold content of an alloy on a scale from 1 to 24, with 24 kt meaning pure gold. For a quick melt value the melt value calculator helps; anyone wanting to value scrap gold or dental gold is best served by the dental gold calculator.