Troy Ounce: Definition, History, and Conversion Table
By StoneX Bullion
If you’ve been looking to invest in precious metals, you may have noticed the term ‘troy ounce’ referring to the weight of coins and bars. This is a unit of measure used for pricing and weighing precious metals like gold, silver, platinum, and palladium. When you see the gold spot price on a chart, it’s usually referring to the price of gold per troy ounce (oz t).
The troy ounce is different to the standard ounce used to measure everyday commodities like sugar and grain. For new investors encountering troy weights for the first time, there can be some confusion and misunderstanding as to how much value they’re getting from a precious metals purchase.
To help you grasp what a troy ounce is and why it’s used in the precious metals industry, we’ve created this guide. Keep reading to learn what a troy ounce is, the history of its use, how you can convert troy ounces to regular ounces, and other common questions.
What is a troy ounce?
A troy ounce is a unit of measure used to weigh precious metals. It is different from an avoirdupois ounce, or a standard ounce, which is used to weigh other commodities such as sugar and grains (and nearly everything else).
Troy ounces have been the official weight system for gold, silver, and other precious metals since the 16th century. They are usually abbreviated to read ‘t oz’ or ‘oz t’. When precious metals are listed on charts or for sale per ounce, this is always referring to a troy ounce. This is important to remember since troy ounces differ in weight from standard ounces.
How much does a troy ounce weigh?
One troy ounce is equivalent to 1.097 standard (avoirdupois) ounces.
In grams this is about 31.103476 grams, as per the UK Royal Mint. The standard ounce weighs slightly less than a troy ounce, coming in at 28.349 grams.
History of the troy ounce
It’s unclear exactly when and where the troy weight system was created, however it’s generally considered to have started in Troyes, France. This was the location of a popular trade market in the Middle Ages that attracted merchants from all over Europe and Britain looking to buy and sell goods. According to the measurement system in Troyes, 480 grains of barley equaled one troy ounce, and there were 12 troy ounces in one troy pound.
An alternative theory states that the troy ounce had its roots in Roman times. The Romans had a monetary system that used bronze bars, which when broken down into 12 pieces would equate to one uncia, or ounce. Each uncia weighed around 31.1 grams, roughly the same as a troy ounce.
In the 10th century, as Europe began to grow into an economic force, merchants from all over the world flocked to Rome to buy and sell goods. To make business easier, a new, standardized monetary weight system was created. It was believed that the monetary system of Troyes was modeled on this Roman system.
Regardless of whether it originated in Troyes or Rome, we know that the system was first used in England in the 15th century. At this time, King Henry II of England, who was born in France, chose to adjust the British coinage system to match that of the French troy system. This system was further developed over time, however the troy ounce remains to be the official standard measurement for gold, silver, and other precious metals in the UK.
In 1828, use of the troy ounce spread to the USA. It’s now accepted as a global standard for measuring the weight of precious metals, helping investors and sellers from all over the world make accurate and consistent transactions.
Troy ounce versus avoirdupois ounce
Although you may have never heard of the term avoirdupois ounce before reading this article, it is the standard unit of measure used to weigh food and nearly everything other than precious metals. Because it’s such a common unit of measure, we’ve dropped the avoirdupois and now simply call it an ounce.
An avoirdupois ounce weighs about 10% less than a troy ounce, with one ounce equivalent to 1.097 troy ounces. One standard avoirdupois pound contains 14.6 troy ounces compared to 16 avoirdupois ounces. In the metric system, one avoirdupois ounce is equal to 28.35 grams while one troy ounce is a slightly heavier 31.1 grams.
If you fancy being a little more confused, a troy pound is lighter than a standard pound. This is because in the troy weighting system, only 12 ounces are needed to make a pound.
While the difference between a troy ounce and an avoirdupois may seem minor, it can add up when measuring larger quantities of precious metals. All you need to remember is that anytime you see the price of precious metals quoted on a chart, it’s referring to troy ounces and not standard ounces. You can do the math from there if you need to.
Troy ounce conversion table
Below is a simple conversion table that shows the equivalence of one troy ounce to other units of measure.
1 Troy Ounce is equal to:
Start investing in precious metals
Anyone interested in investing in precious metals should be aware of the difference between a troy ounce and an avoirdupois ounce.
There are four main precious metals measured by the troy ounce: gold, silver, platinum, and palladium. You likely already know the value of gold and silver, which have been used for centuries to preserve and grow wealth.
The other two precious metals are less widely recognized for their investment potential but still hold a lot of value:
- Platinum: Platinum is a silvery-white metal that’s relatively new to the precious metals scene. It was first ‘discovered’ by Europeans in South America in the 18th century and has since been used in various ways, from the chemical industry to automotive and jewelry-making.
- Palladium: Palladium in its pure form is rarely found in nature. It is usually extracted from other metals such as platinum, copper, or zinc, and is widely used in the medical, dental, and electronics industries.
Each precious metal is valuable in its own way and all make excellent investments.
Troy ounce FAQs
To help you gain a thorough understanding of troy ounces and how they work in the precious metals industry, we’ve answered some frequently asked questions below.
Is 1 oz heavier than 1 troy ounce?
A troy ounce is heavier than a standard ounce by around 10%. One troy ounce equals approximately 1.097 standard ounces.
What is a troy pound?
A troy pound is equal to 12 troy ounces. It is lighter than a standard pound, with one troy pound equating to 0.823 pounds. The reason that troy pounds are lighter than avoirdupois pounds, when troy ounces are heavier, is that the troy pound is made up of 12 ounces instead of the usual 16.
What are troy ounces used for?
Troy ounces are used to measure the weight of precious metals, such as gold and silver, as well as some gemstones. Pretty much everything else is weighed using the metric system or standard ounces.
Why is it called a troy ounce?
It’s said that the term ‘troy ounce’ is derived from the city Troyes in France. This was the location of a popular trade market in Europe, where the troy unit of measure was widely used for its accuracy and consistency.
What’s the difference between a standard ounce and a troy ounce?
Besides their weight differences, troy ounces and standard ounces are used for different purposes. The troy ounce is mainly used to weigh precious metals and some gemstones while standard ounces are used for everyday commodities.
Why is it important to know troy ounces in precious metals?
A troy ounce is the global standard for buying, selling, and trading precious metals. Its use helps ensure that transactions from all over the world are uniform and consistent. Prices of precious metals are always quoted and traded based on their weight in troy ounces. For example, when you see the price of gold in ounces, this is always referring to a troy ounce. This is important for investors to note as it ensures they are correctly estimating the value of their assets.
Are other troy weight units used in precious metals?
Yes, as well as the troy ounce there are other units within the troy system used in the precious metals industry. These units are pennyweights and grains, usually used to measure smaller quantities of precious metals. Twenty pennyweights is equal to one troy ounce, and one troy ounce is made up of 480 grains.
Why should precious metals investors know the troy ounce?
Understanding what a troy ounce is, and how it compares to a regular ounce, is essential for anyone buying or selling precious metals. It prevents confusion or miscalculation when trading precious metals and ensures people can accurately measure and price their assets.
In summary, troy ounces are a unit of measure used in the precious metals market to weigh gold, silver, platinum, palladium, and some other gemstones. They are slightly heavier than standard ounces, with around 1.097 troy ounces in a standard ounce.
Now that you understand what a troy ounce is and how it’s different to other units of measure, you can start your investment journey off smartly, knowing exactly how much value you’ll be getting from each investment and avoiding any misunderstandings along the way.
At StoneX Bullion, all of our precious metals are listed using the troy system. Whether you're looking to buy rare coins, gold bullion, or platinum and palladium, you’ll find investment-grade precious metals ready to crown your collection and preserve your wealth for years to come.