Carat (Gold Fineness)
Also: kt, ct, Carat gold, Gold carat
Carat (abbreviation kt or ct) is the traditional unit of measurement for the gold content of an alloy: 24 carat corresponds to pure gold (999 fineness, highest trading purity 999.9).
The carat (abbreviation kt, more rarely ct) is the oldest unit still in common use in the jewellery and coin trade to express the proportion of gold in an alloy. The scale ranges from 1 kt to 24 kt, where 24 carat means pure gold. It should not be confused with the identically named carat as a unit of weight for diamonds and gemstones, which has a completely different meaning.
Origin and background
The term derives from the Arabic qirat and the Greek keration (carob seed) - a historical weight standard. In the Middle Ages the idea became established of subdividing gold into 24 equal parts, because the Byzantine gold solidus weighed 24 siliquae. This subdivision has persisted to this day: each carat corresponds to one twenty-fourth of the total weight of the alloy.
Conversion: carat to fineness (per mille)
The fineness indicates how many grams of pure gold are contained in 1,000 grams of the alloy. The conversion is straightforward:
Fineness = carat number x (1,000 / 24)
Example 18 kt: 18 x (1,000 / 24) = 750
Overview of the most common gold alloys
| Carat | 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 | Widely used jewellery standard |
| 9 kt | 375 | 37.5 | Standard in the United Kingdom |
| 8 kt | 333 | 33.3 | Low-fineness jewellery gold |
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 little suited to most everyday objects. By alloying with other metals, hardness, colour and workability are deliberately controlled:
- Copper increases 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 + copper together are the classic mix for jewellery gold
The lower the carat value, the higher the share of these alloying metals.
Hallmarks and stamps
Across the EU, gold items above a certain weight are commonly marked with a fineness hallmark. Common are the per-mille values (e.g. 585, 750, 999), while the carat indication is more widespread outside continental Europe - especially in the USA and the United Kingdom. Historical pieces often still carry carat indications as a punch mark.
Carat in investment gold
For investment gold in the VAT-exemption sense under EU law (Directive 2006/112/EC), a gold bar must have a fineness of at least 995 (corresponding to roughly 23.88 kt) and gold coins at least 900 (corresponding to 21.6 kt). Bullion coins such as the Krugerrand at 916 (22 kt) meet this requirement. In Malta such investment gold is VAT-exempt, whereas silver, platinum and palladium are subject to the 18% standard VAT rate. Note: this is not tax or investment advice; for individual questions please consult a tax adviser.
The material value of a gold alloy can be determined quickly: in the gold calculator you enter weight and carat and obtain the current melt value based on the spot price.
Distinction: carat (diamond) vs. carat (gold)
| Feature | Carat (gold) | Carat (diamond/gemstone) |
|---|---|---|
| Meaning | Purity (proportion) | Weight |
| Scale | 1-24 | from 0.01 ct upwards |
| Unit | dimensionless (ratio) | 1 ct = 0.2 grams |
| Abbreviation | kt (or ct) | ct |
You can find further background on the carat as a weight measure in the glossary entry on diamond weights.
Key takeaway
Carat measures the gold content of an alloy on a scale from 1 to 24 - 24 kt means pure gold. For the quick melt value the melt value calculator helps; anyone wishing to value scrap gold or dental gold is best served by the dental gold calculator.