Gold purity

Understanding gold purity is essential for getting an accurate valuation of an item. In most cases the purity of a gold item should be hallmarked or indicated in some other way, but below we discuss how gold purity is denoted, and some of the common figures you should see.

Pure gold is extremely soft and malleable. It is because of this that manufacturers, typically jewellers, often mix or alloy pure gold with other harder base metals. Without knowing a gold item’s precious metal content it is difficult to arrive at a true valuation, as such the purity of an item is an essential piece of information to have.

To quantify this there are two major systems that measure gold purity. They are karat (carat outside the US), and fineness. Both karat and fineness give figures that indicate the proportion of pure gold to other base metals in gold jewellery and products.

Gold karat

Karat expresses the proportion of gold to other metals in parts of 24. In this system, 24 karat is pure gold with the figures moving down from there. 9 karat is nine parts gold: with the remaining fifteen parts of the 24 being composed of other metals. 9 karat gold is the lowest purity typically found in common usage, with anything lower no longer truly being considered gold.

Gold fineness

Fineness, in gold, silver and other precious metals, expresses the percentage of gold to other metals in parts per thousand. It is therefore a much more precise scale than karat and far easier to understand at a glance. In this system, 999.9 is pure gold, equivalent to 24 karat as mentioned above. 9 karat gold, nine parts gold to fifteen parts other metals, is 375 fineness.

In the UK, with the exception of coins and pure gold bars, any manufactured gold products weighing over 1 gram or 0.0321507 troy ounce must be hallmarked with the item's fineness.

Common gold purities

How many karats is pure gold?

Both 24 karat and 999.9 fineness are generally accepted as pure gold. Despite this, in truth it is impossible to produce 100% pure gold based on current technical limits. Removing any tiny molecules of other material is not achievable, and would prove extremely expensive and difficult to even prove. This is why, in common terms, pure gold is 999 or 999.9 not 1,000 fineness.

The most pure gold ever was made in 1957 by Australia's Perth Mint. This was 999.999 fineness, known as 'six nines fineness'. It has since been used by The Royal Mint as its benchmark for purity.

Gold bars

995 fineness is the minimum allowed purity for gold investment bars and is used as raw material for further gold alloying. The London Bullion Market Association undertakes gold testing and produces a 'Good Delivery List' that specifies standards for gold investment bars, which includes the required fineness.

All BullionByPost, bars are pure 24 karat gold and manufactured by refiners approved by the London Bullion Market Association. Coins will be a mix of 24 karat or 22 karat depending on the coin, but we show the fineness of all products in their specification section.

Minimum purity

Generally, when describing items as gold, we are in truth referring to gold alloys. There are limits at which items, such as jewellery, contain so little gold they can no longer be called gold.

This minimum gold purity varies by country. In the US, 10 karat or 417 fineness is the legal minimum. In France, the UK, Austria, Portugal and Ireland, 9 karat or 375 fineness is the minimum that can be called gold. In Denmark, Germany and Greece it is even lower at 8 karat or 333 fineness.

Below is a chart of the most commonly found gold purity in various applications and countries:

Gold Purity Fineness Karat
99.9% 999 24k
99.5% 995 24k
95.83% 958.3 23k
91.6% 916 22k
90% 900 21k
83.4% 834 20k
75% 750 18k
58.5% 585 14k
41.7% 417 10k
37.5% 375 9k
33.3% 333 8k