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 and, in the jewellery and coin trade, still the most common unit for expressing the gold content in an alloy. The scale runs from 1 kt to 24 kt, with 24 carat meaning pure gold. It is not to 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 qīrāṭ and the Greek kerátion (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 survived 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 × (1,000 ÷ 24)
Example 18 kt: 18 × (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 | Minimum standard in some continental European countries |
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 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 produce white gold (often additionally rhodium-plated)
- Silver + copper together are the classic mixture for jewellery gold
The lower the carat value, the higher the proportion of these alloying metals.
Hallmarks and Stamps
In the United Kingdom, gold articles above a certain weight must be hallmarked at an official Assay Office, which records the fineness (e.g. 375, 585, 750, 999). The fineness stamp shows the per-mille value, while the carat designation is more common colloquially, especially in the UK and USA. Historical pieces often still carry carat figures as a hallmark.
Carat in Investment Gold
For investment gold in the tax sense (VAT-exempt under HMRC rules, per EU VAT Directive 2006/112/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 at 916‰ (22 kt) meet this requirement. Note: this is not tax or investment advice; for individual questions please consult a qualified adviser.
The material value of a gold alloy can be determined quickly: in the Gold Calculator you enter the 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 |
Further background on the carat as a weight measure can be found in the glossary entry on diamond weights.
In Brief
Carat measures the gold content of an alloy on a scale from 1 to 24 – 24 kt means pure gold. For a 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.