The Ultimate Guide on Gold Purity Measurements

If you’ve shopped for gold jewelry and other products, you’re probably familiar with the term karat or carat (abbreviated K or kt). Karat is the most commonly used measure of gold purity, and its scale ranges from 0 to 24.

A karat signifies the percentage of gold present in a piece of metal. It is  1/24  part or 4.1667% of the whole. Pure gold is 24 karats, and a product that contains 14 parts gold and ten parts other metal is 14-karat gold, or 58.33% gold.

Likewise, an item with a purity of one karat encompasses 1 part gold and 23 parts other metals or alloys, or 4.16% gold. To convert karats to a percentage, divide the karat value by 24, then multiply the result by 100.

Besides karat, gold purity can also be expressed in millesimal fineness, indicated by parts per thousand of genuine gold by mass in an alloy. All of these are used as gold purity measurements. Let’s find out more about it!

Common Terminology Used in Gold Purity Measurement

  • Gold purity or fineness: gold-to-metal additive ratio
  • Bullion: precious metal in its bulk form, such as gold bars, expressed in mass instead of value
  • The assay: test that determines metal content and quality
  • Carat: unit of measurement for precious stones equivalent to 200 grams
  • Karat: unit of measurement for gold purity—the higher the number of karats, the finer the gold, with 24 karats being the finest
  • Hallmark: a symbol stamped on a piece of precious metal to certify its standard of purity
  • Millesimal fineness: system that indicates the purity of precious metal by parts per thousands instead of karats
  • Troy ounce: equals 31.1034 grams, or about 1.09714 avoirdupois ounces
  • Troy weight: system for measuring precious metals and gemstones—a whole troy pound is equivalent to 12 troy ounces instead of the 16 avoirdupois ounces contained in a standard pound

Measuring Gold Purity Using Karats

Understanding how to calculate the gold content of your product is essential when shopping for gold products. You can achieve this by knowing the number of karats in your piece of gold.

The following conversion chart will make it easy for you to calculate the purity of your gold.

Number of Karats (K) Parts of Gold Gold Purity (%) Millesimal Fineness
8 8/24 33.3 333
10 10/24 41.7 416 – 417
12 12/24 50.0 500
14 14/24 58.3 583 – 585
18 18/24 75.0 750
22 22/24 91.7 916 – 917
24 24/24 99.9 999


We observed earlier that karats are the ratio of gold to other metals or alloys in your gold product. On the other hand, millesimal fineness is the percentage of gold expressed in parts per thousand.

It’s also worth noting that a higher karat doesn’t necessarily mean you have a better quality gold. It only means that you have a more pure, more expensive gold. Keep in mind that the less pure the precious metal is, the more alloys it contains.

The higher the number of alloy metals, the stronger the gold. Jewelry manufacturers prefer this type of gold to 24-karat gold. Pure gold is highly soft and vulnerable to damage.

However, a higher karat gold resists tarnishing much better than lower karat gold. What’s more, a higher carat gold has more value than its lower karat counterpart. By keeping these points in mind, you’ll have an easier time choosing the purity level that best suits your needs.

Simple Ways To Determine Gold Purity

three gold bars put together


It’s advisable to buy your precious metal from a reputable dealer to avoid the risk of purchasing counterfeit gold. However, knowing how to test the purity of gold can also save you many hassles. Here are some simple techniques to perform at home to determine if your gold is authentic.

The Magnifying Glass Test

This is perhaps the most straightforward test for gold at home. You only need a magnifying glass and your precious metal. Inspect your gold item methodically using the magnifying glass for these visual signs:

  • Signs of discoloration – Environmental factors don’t affect the properties of gold. If you notice any discoloration marks on your gold, then it’s gold-plated or fake gold.
  • Strange color and shininess – Gold features an attractive soft yellow color and is not extremely shiny. If you have a shiny, yellow, or reddish piece, then it’s not pure gold.

Hallmark or Stamp Test

Another simple home test for gold is the hallmark test. You may also require a magnifying glass to inspect any gold hallmarks or jewelry markings on your gold product. You can find the markings on the surface or near the clasp of your item.

These markings should indicate at least the purity of gold in karats or millesimal fineness. Some gold jewelry also comes with the manufacturer’s stamp. You should be wary of the following hallmarks as they are an indication of a gold-plated product:

  • HGP
  • GF
  • HEG
  • GP
  • GEP
  • RGP

Also, avoid gold items that contain the numbers 800, 925, and 950 because they’re silver hallmarks. Otherwise, you may end up buying fake gold. The hallmark test is not 100% foolproof, so you can only use it to determine if the gold isn’t pure or authentic. You might want to try other tests if you have doubts about your gold’s authenticity.

The Acid Test

The acid test works by harming artificial materials in your precious metal. A nitric acid test cannot affect the properties of pure gold. Start the test by making a small mark on your gold piece to penetrate the surface. Add a drop of nitric acid to the spot and see how it reacts.

Fake gold will instantly turn green on the spot the acid touches. Genuine gold won’t react to the acid, leaving you with a transparent liquid with no color change.

The Magnet Test

If you’re looking for a convenient and portable test for gold purity, the magnetic test is a perfect option. You can easily carry the magnet around in your pocket. So, how does the magnetic test work?

A magnet doesn’t attract pure gold, while fake gold and various alloys will attract the magnet. If you unknowingly purchase a piece of item that looks like gold, this test can help identify the underlying metal.

The Float Test

This test only requires placing your gold product in a cup of water. Gold has a high density of 19.32 g/ml, so genuine gold will instantly sink in the water. Fake or gold-plated items usually hover or float on the surface. You should expect a gold alloy to tilt up halfway. The float test is not 100% accurate because some fake items may contain other heavy metals that sink in water.

You might want to consider trying another test if your piece sinks, but you still doubt its authenticity. If your item rusts or gets discolored over time, it’s undoubtedly fake.

Advanced Techniques for Testing Gold Purity

jeweler checking gold purity


If you have difficulties testing your gold at home, you can hire a reputable gold dealer or jeweler to help you test the purity of your precious metal. Here are some of the advanced techniques that professionals use to identify fake gold.

Melting and Sampling Spectrum Detection

While this technique is expensive, it is one of the most comprehensive. It capitalizes on a thermal-analytical technique called Differential Scanning Calorimetry. It involves placing a sample of the piece to be tested in a Differential Scanning Calorimeter and subjecting the sample and reference piece to the same temperature intensity. This technique helps to identify fake gold as it will have significantly varying heat properties from genuine gold.

Metallographic Analysis and Smelting Identification

The metallographic analysis technique applies the concept of metallography to detect fake gold and usually involves optical microscopy or scanning electron microscopy. Smelting consists of melting the piece of gold to be tested. Fake gold will only produce other metals like zinc and copper after the melting process.

X-Ray Fluorescence (XRF)

This technique is probably the simplest among the advanced gold detection options. It involves the emission of an X-ray photon beam that hits the atom of the piece being tested. Once the beam collides with the sample atom, electrons of various elements produce varying energy intensities. If your gold contains other elements, it will release different intensities of energy, confirming its fakeness.


If you aren’t careful, you may end up spending money on fake jewelry and metal blends, thinking you are investing in pure gold. According to most global standards, anything containing less than ten karats or 41.7% of gold is considered fake. A reputable gold dealer or jeweler can help you determine the authenticity of gold.

If you want to learn more about gold and gold-related investments, Oxford Gold is the right website for you. We have all the information you need to make the right decisions about gold investment. If you’re looking to invest in gold, visit our website to find out how our gold investment plans can help you achieve your investment goals.



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