Jan 2024


Jan 2024

Gold Purity, Fineness, And Karat – What Is It And How To Check It

By StoneX Bullion

Understanding gold purity, whether in jewelry, gold coins, or gold bullion bars, is essential to making informed decisions as an investor. Measured in karats or fineness, gold purity helps you accurately assess the value of your gold investments.

In this article, we discuss what gold purity is, how it’s measured, and explore each of the karat and fineness systems. We also talk about why it’s important to check gold purity and a few methods you can use to determine the purity of your gold investments. Let’s begin!

What is gold purity?

Gold purity refers to the amount of pure gold present in gold jewelry, gold bullion coins, and gold bars compared to other alloys.

Because pure gold is so soft and malleable, it’s often mixed with other metals like silver, copper, zinc, or palladium to enhance its durability and strength. The more a piece of gold is mixed with other alloys, the less pure it is.

When buying gold bars and coins for investment, high purity is paramount. It ensures there’s minimal impurities, enhances the investment’s liquidity and saleability, and assures investors of the asset’s value and quality. With jewelry, lower purity gold can be more suitable as it enhances durability and strength, making it more appropriate for everyday wear.

How is gold purity measured?

While the weight of gold is measured in troy ounces, its purity is measured in either karats (k or ct) or fineness.

  • Karat system: This represents the proportion of gold to other metals in 24 parts. 24 karat gold is the purest form of gold while 18 karat gold, for example, contains 18 parts pure gold to 6 parts other metals.
  • Fineness: Fineness refers to the purity of gold in parts per thousand, usually expressed as a decimal fraction or percentage. Pure, unadulterated gold has a fineness of 1000 though it’s rare to encounter gold of this purity. Gold with a fineness of 0.950 means it contains 950 parts gold out of 1000, otherwise expressed as 95% pure gold.

The karat system is most often used in reference to gold jewelry while fineness is more used for investment-grade gold coins and bars. We’ll explore each of these measurement systems below.

What are karats in gold?

Karats, often denoted as ‘k’ or ‘ct’, are a measurement used to indicate the proportion of pure gold compared to other metals. It uses a 24-part system to express gold purity with 24 karats denoting more pure gold alloys. As the karat number decreases, the number of other metals increases, for example:

  • 24 karat gold: Pure gold with no other metals added
  • 18 karat gold: Contains 18 parts pure gold with 6 parts other metals (75% pure gold)
  • 14 karat gold: Contains 14 parts pure gold with 10 parts other metals (58.3% pure gold)
  • 10 karat gold: Contains 10 parts pure gold to 14 parts other metals (41.7% pure gold).

The karat system is widely used in the jewelry industry to represent the purity of gold items. Higher karat gold is generally considered more valuable, however it can be more prone to scratching or damage due to its malleability. Lower karat gold is generally more appropriate for everyday use.

What is fineness in gold?

Like the karat system, fineness is used to measure the purity of gold in items such as gold bullion coins and gold bars. It’s often expressed as a decimal or percentage. Unlike the 24-part karat system, fineness divides an alloy into 1000 parts and refers to the amount of pure gold within those 1000 parts.

The purest gold is considered to have a fineness of 1.000 or 100%, meaning no other metals are mixed in. However, it’s essentially impossible to produce 100% pure gold. This is because it’s difficult to prove that there are no slight traces of other materials in a gold item. For that reason, 99.99% or 999.9 fineness is generally considered to be the most pure form of gold.

Generally, the purest gold you will encounter in gold bars, coins, or jewelry, has a fineness of 999.9 (also expressed as 0.9999) or 99.99% (also known as four nines fine gold).

  • Take the 100g C. Hafner gold bar, for example. With a purity of 999.9, it holds up as an excellent investment-grade gold bar.
  • A gold coin with a fineness of 916.7, such as the ½ oz Gold Krugerrand coin, will contain 91.7% pure gold and 8.3% other metals, and so on.

Karats versus fineness

The main difference between karats and fineness is that the gold karat system relies on 24 parts while fineness measures purity in parts per 1000.

Because fineness divides a gold item into so many more parts than the karat system, it offers a more accurate measurement of gold purity. This is why it’s the universally accepted standard for measuring the purity of investment-grade gold. Having such precise measurements of gold purity allows investors to clearly understand the quality and value of their assets.

The karat system, on the other hand, is much more consumer-friendly as it relies on less precise measurements. This is why it’s used for jewelry and other consumer products.

Below is a chart that compares karats to fineness.




0.9999 (99.99%)


Investment gold bars and gold bullion coins

0.9583 (95.83%)


Gold coins and expensive jewelry

0.916 (91.6%)


Expensive jewelry

Gold used in dentures

Great Britain’s golden coins

0.750 (75%)


Fine gold jewelry

0.585 (58.5%)


Common jewelry

0.500 (50%)


Cheap jewelry

What is the minimum content of gold?

Interestingly enough, an item cannot be referred to as gold when its purity is below a certain level. For jewelry to be legally marketed and sold as gold, it usually needs to have a minimum gold content. This differs between countries:

  • In the United States, 10 karat is the legal minimum for an item to be called gold.
  • In France, UK, Austria, Portugal, and Ireland, 9 karats is acceptable as gold.
  • In Denmark, Germany, and Greece, 8 karat is the legal minimum standard for an item to be considered gold.

In the context of investment-grade gold bars, 995 fineness is the minimum purity allowed, although most gold bars will have 999.9 purity, as with the 500g PAMP Fortuna gold bar. Gold coins will generally range in purity from 916 (22 karats) to 999.9 (99.99%) pure gold.

Why should you check gold purity?

Checking the purity of your gold investments is important for several reasons:

  • Determine its value: Gold’s value is directly affected by its purity. Knowing how much pure gold is in your jewelry, gold coins, or gold bar investments helps you understand how much it’s worth. To get the best price when selling your gold, it's essential that you know its purity and weight - both factors that determine gold's price.
  • Check authenticity: Verifying purity can help you confirm the authenticity of your gold investments and make sure you’re getting what you paid for. Especially when it comes to investment-grade gold coins, checking for purity can help you avoid buying counterfeits or fakes.
  • Understand durability: Gold purity affects the durability and appearance of gold jewelry and coins. If you’re buying gold jewelry for everyday wear, it may be more suitable to choose one with lower purity so that it’s more durable and less susceptible to damage. If you’re investing in gold bars or coins, understanding its pure gold content can help you choose the best storage solution to preserve its value.
  • Investment purposes: It goes without saying that when you’re investing in gold, purity is essential. Gold bullion or bars with high purity are more desirable and have more market value.

How to check gold purity

There are several ways you can check the purity of gold, ranging from simple at-home tests to more sophisticated methods used by professionals. Below we’ve listed some of these methods for checking gold purity:

  • Hallmark stamps: Many gold items, especially gold coins and bars, are stamped with hallmarks that indicate their purity. These stamps usually display fineness or karat value.
  • Professional assay: For the most accurate assessment of gold purity, visit a professional jeweler or assayer. These are experts in determining gold value and will use professional equipment such as X-ray fluorescence (XRF) machines or fire assay methods to precisely determine gold’s purity.
  • Price: When buying gold, check the value of gold on the market. If the gold you are buying is being sold for a suspiciously low price, then there’s a chance its purity is low or it’s a fake.
  • Electronic gold testers: These devices use electrical conductivity to assess the purity of gold. They provide quick results and are relatively accurate, however results may be skewed when checking the purity of gold plated items.
  • Magnet test: This test won’t determine the purity of a gold item but will help you identify non-gold metals that may be present. Unlike many other metals, gold is not magnetic. You can use a strong magnet to see if your gold item is attracted to it. Note that copper, silver, and aluminum are also non-magnetic metals.

Each of the above methods has its advantages and limitations. For a simple, at-home check, hallmark stamps and magnet tests can give you an initial indication of gold purity. For more valuable or investment-grade gold, it’s always recommended to take it to a professional for accurate assessment.

Gold purity and different gold colors

Mixing gold with other alloy metals doesn’t just enhance its durability, it can also change its appearance. While most of us recognize gold to be yellow color, there can be other variations to its color:

  • White gold: Created by combining pure yellow gold with metals like silver or palladium. It’s also often plated with rhodium to create a stronger surface shine.
  • Rose gold: Created by combining pure gold with copper, resulting in a soft-pink sheen.
  • Black gold: Created by combining pure gold with cobalt oxide.

Buy pure gold, securely

Start your gold investment journey with high quality investment bars and coins from StoneX Bullion. We stock a wide range of pieces to suit all kinds of investors, from those looking for small, collectible coins to people ready to preserve their wealth with high-purity gold bars.

All of our products come from the best-known mints in the world, stored in a high-security vault and delivered to your home safely and securely. Whether you're looking to invest in bullion for your future or a special coin to crown your collection, you'll find it here at StoneX Bullion.