If you aren’t familiar with troy or avoirdupois ounces, you aren’t alone. Here are the differences between some common bullion conversions.

Precious Metal Conversions

The value of a coin, jewel, or anything else made from a precious metal like gold or silver depends on its mass and purity. An item made of pure gold is going to be more valuable than something made from a gold alloy, for example. The more mass a sample of precious metal has, the more that sample will be worth.

The mass of a precious metal is discovered through the use of precious metal conversions, and the type of conversion used typically depends on the type of metal being measured.

Troy Ounces vs. Avoirdupois Ounces

The troy ounce is a unit of measurement used to describe the mass of precious metals. It is slightly larger than the avoirdupois or “regular” ounce; a single troy ounce equals 1.1 avoirdupois ounces. Twelve troy ounces equal one troy pound, but the troy pound measurement is rarely used anymore. As people outside the United States often use units from the metric system, the troy ounce also equals 31.1 grams.

The avoirdupois ounce is not usually used to measure precious metals, but it can be used to measure base metals like copper. One avoirdupois ounce equals 28.3 grams, and 16 avoirdupois ounces equal one avoirdupois pound (or 453.6 grams).


The kilogram is a unit of measurement from the metric system that equals 1,000 grams. One kilogram roughly equals 2.2 pounds or 32 troy ounces. People sometimes use kilograms when selling or buying precious metals in bulk. When trading precious metals, they will use kilograms when measuring bars made of platinum, palladium, silver, or gold.

Measuring Purity

Like measurements of mass, there are also measurements of metal purity. A karat is perhaps the most common purity conversion. The word can also be spelled “carat,” but a carat is more commonly used to measure diamond weight.

Karat is most commonly used in reference to gold, and it describes the ratio of gold to another metal. The numbers in the ratio always add up to 24, so an item described as having 24 karats (24k) is 100% pure gold. Thus, gold bullion will always be 24k. An item described as 18k will be 18 parts gold and six parts something else, while an item described as 14k will be 14 parts gold and 10 parts something else, and so on. Since pure gold is extremely soft, most gold jewelry will be between 14k and 18k.

The millieme (‰), or thousandth, is another unit for measuring the purity of a metal, and it is derived from the metric system. The higher the number, the purer the metal is. However, as it is physically impossible for a metal to be completely pure, a pure metal is described as 999 milliemes rather than 1,000 milliemes. Such purity is mainly seen in metal bars since pure precious metals are too soft and easily deformed to be used in making other items. Pure silver, for example, is so soft it is difficult to transport it without losing its shape. Because of this, the purest metals are traded and stored by banks and other financial institutions.

The millieme can be converted into percentages or karats. Since one millieme equals 1/1000 while one percent equals 1/100, converting milliemes into percentages is straightforward: 10 milliemes equals 1 percent, while 750 milliemes equal 75 percent, and so forth. Converting percentages into milliemes simply requires multiplying the percentage by 10, while converting milliemes into percentages requires dividing the millieme by 10.

Converting milliemes into karats is somewhat trickier since it is not always possible to get a round figure. While 18 karats equal 750 milliemes, 22 karats equal 916.666 milliemes. A single karat equals around 41.6667 milliemes. Converting milliemes into karats requires multiplying the milliemes by 24 (750 x 24 = 18,000) and then dividing the result by 1,000 (18,000 ÷ 1,000 = 18 karats). Converting karats into milliemes requires dividing the karats by 24 (18 ÷ 24 = .75) and then multiplying the result by 1,000 (.75 x 1000 = 750 milliemes).

Most mints will stamp the purity and weight on all the bars and coins they produce. Jewels and decorative objects made from precious metals will also have a purity stamp on them even if it is not always easy to find.

Just How Pure is Precious Metal Bullion?

As mentioned earlier, the very purest metals will be bars owned by financial institutions. Platinum is typically measured in either milliemes or percentages. Platinum jewelry generally ranges from 80 to 95 percent platinum, or 800 to 950 milliemes.

Silver is also usually measured in percentages or milliemes. Sterling silver is 92.5 percent silver, or 925 milliemes, with the remaining 7.5 percent usually being copper. It is generally used to make high-end silverware or jewelry. Coins range in purity from 90 to 95.8 percent or 900 to 958 milliemes. Less valuable jewelry or silverware contains 800 to 825 milliemes of silver.

Gold has many uses and thus comes in many levels of purity. Industrial gold like that used to make electronic circuitry is only a little more than 20 percent gold. It has 5 karats or 200.8 milliemes. The gold used in dentistry is actually 33.3 percent to 37.5 percent gold and has 8 or 9 karats. Costume jewelry has a similar purity. Real gold jewelry ranges from 14 to 18 karats or 583 to 750 milliemes. Gold coins are at least 91.6 percent gold or 22 karats.

The different types of colored gold are never pure gold. White gold, for example, is actually 75 percent gold and 25 percent palladium or nickel, while rose gold is 75 percent gold and 25 percent copper.

Whether you’re interested in investing in gold, silver, or another type of precious metal, Provident Metals has a wide selection to choose from.