When buying gold — whether coins, bars, or jewellery — you'll encounter a range of numbers and terms describing purity: 24 carat, 22 carat, 999.9, 916, 750. Understanding what these mean is fundamental to making informed purchasing decisions and knowing exactly what you're getting for your money.
Gold purity describes the proportion of pure gold in a piece relative to other metals. Pure gold is too soft for most practical uses, so it's typically alloyed with other metals like silver, copper, or zinc to add durability. The purity of the resulting alloy determines its value, its colour, and its suitability for different purposes. In this guide, we'll explain every gold purity system used in the UK and internationally, what the hallmarks mean, and which purity is best for bullion investment.
Gold purity is expressed in two main ways in the UK: the carat system (used primarily for jewellery) and the fineness system (used for bullion coins and bars). Both describe the same thing — the proportion of pure gold — but use different scales.
The carat system divides gold into 24 parts. Pure gold is 24 carat (24ct), meaning all 24 parts are gold. 18 carat gold contains 18 parts gold and 6 parts other metals. The carat system is most commonly used for gold jewellery in the UK and is the system most consumers are familiar with.
The fineness system expresses gold purity in parts per thousand. Pure gold is 999.9 fine (sometimes written as .9999 or 999.9/1000). This system is the international standard for investment-grade bullion coins and bars. When you see a gold bar stamped with 999.9, it means 999.9 parts per thousand — or 99.99% — are pure gold.
Here are the most common gold purity grades you'll encounter when buying gold in the UK:
This is the highest purity commercially produced at scale and the standard for modern investment bullion. It contains 99.99% pure gold. Products at this purity include our 1oz Gold Bar, PAMP Suisse 5g Gold Bar, 20g Gold Bar, Valcambi 1g CombiBar, and Australian Gold Kangaroo. The deep, rich yellow colour of .9999 fine gold is immediately recognisable and highly desirable for investment purposes.
Slightly below .9999, this grade contains 99.9% pure gold and is used for some gold bars and coins. The difference in gold content between .999 and .9999 is minimal — just 0.09% — and both are considered 24 carat gold. For investment purposes, both grades are excellent choices.
This is the standard for British gold coins, including the iconic Gold Sovereign and the South African Krugerrand. It contains 91.67% pure gold, with the remainder typically being copper and silver. The 22 carat alloy is harder and more durable than pure gold, making it ideal for coins that may be handled regularly. Historic Sovereigns in our range — including the 1884 Victorian Sovereign, 1912 George V Sovereign, and 1927 George V Sovereign — are all struck in 22 carat gold.
18 carat gold contains 75% pure gold and is the standard for fine jewellery in the UK and internationally. It offers a good balance of gold content, durability, and workability. 18ct gold is available in yellow, white (alloyed with palladium or nickel), and rose (alloyed with copper) varieties.
14 carat gold contains 58.5% pure gold and is common in European and American jewellery markets. It's more durable than higher-purity alloys and less expensive, making it popular for everyday jewellery.
9 carat gold contains 37.5% pure gold and is the minimum legal standard for gold in the UK. It's the most common grade for everyday jewellery sold on the high street, offering durability and affordability at the cost of lower gold content.
In the UK, gold items above a certain weight must be hallmarked by an approved Assay Office before being sold as gold. The UK hallmark system is one of the oldest consumer protection systems in the world, dating back to 1300. A full UK hallmark contains up to four components:
The maker's or sponsor's unique registered mark, identifying who submitted the item for hallmarking. This is typically the manufacturer or importer.
Identifies the metal (a crown symbol for gold) and the fineness in a shield-shaped cartouche. Common marks: 999 (24ct), 916 (22ct), 750 (18ct), 585 (14ct), 375 (9ct).
Identifies which of the four UK Assay Offices tested the item: London (leopard's head), Birmingham (anchor), Sheffield (rose), Edinburgh (castle). The London Assay Office is located near our Hatton Garden premises in Goldsmiths' Hall.
A letter indicating the year of hallmarking. Now optional but still used by some offices and valued by collectors for dating pieces accurately.
Investment bullion coins from recognised mints — the Royal Mint, Perth Mint, US Mint, and others — are exempt from UK hallmarking requirements. Their purity is guaranteed by the issuing mint and is internationally recognised. The assay card accompanying bars like our PAMP Suisse bars serves the same authentication function as a hallmark, and PAMP's Veriscan® technology provides an additional layer of verification.
Gold's purity directly affects its colour, which is an important consideration for both investors and jewellery buyers. Pure 24 carat gold has a rich, deep yellow colour that is immediately recognisable. As other metals are added, the colour changes depending on the alloy:
For pure bullion investment, higher purity means more gold per gram — which is generally preferable. However, purity is not the only factor that matters for UK investors:
A 22 carat Gold Sovereign is completely CGT-free as UK legal tender. A 24 carat gold bar is subject to Capital Gains Tax on profits above the £3,000 annual allowance. For a higher-rate taxpayer making significant gains, the 24% CGT saving on a Sovereign can far outweigh the small difference in gold content between 22ct and 24ct. Read our CGT guide for full details.
22 carat coins are harder and more resistant to scratching and wear than pure gold coins. For coins that will be handled, stored, and potentially resold multiple times, the durability of 22ct is a practical advantage.
Sometimes lower-purity coins carry lower premiums over spot, offering better value per gram of pure gold. Always calculate the effective cost per gram of pure gold when comparing products of different purities.
For more guidance on buying gold, explore our related guides: How to Verify a Gold Coin Is Genuine, Understanding Silver Purity Grades, New vs Pre-Owned Bullion, Gold Bars by Size, and What is a Gold Sovereign?. Browse our full authenticated range of gold coins and bars at 888 Bullion, or visit our Hatton Garden premises for expert advice.
