If you’re looking at buying gold, silver, or other precious metals, you’ll need to know the difference between troy oz vs ounce and how the troy weight system works.
This article covers the differences and measurements in the precious metals industry.
What’s the difference between a troy and regular ounce?
The troy ounce weighs 31.1035 grams, while the avoirdupois ounce (the standard ounce you use for groceries or body weight) weighs 28.3495 grams. That makes a troy ounce about 10% heavier than a regular ounce.
Here’s a quick comparison:
| Measurement unit | Weight in grams | Weight in troy zz | Weight in avoirdupois oz |
|---|---|---|---|
| 1 troy ounce | 31.1035 g | 1.000 | 1.097 |
| 1 avoirdupois ounce | 28.3495 g | 0.911 | 1.000 |
| Weight difference | 2.754 g | 0.089 | 0.097 |
One troy ounce equals about 1.097 regular ounces. Because the precious metals market uses troy ounces, that small difference can add up when you’re buying larger amounts. Knowing this helps make sure you’re actually getting what you paid for.
Where did the troy ounce come from?
The troy weight system goes back to medieval Europe, to the trade fairs in Troyes, France, during the 1100s and 1200s. Merchants from all over Europe needed a common way to measure valuable goods like precious metals and spices.
They used barley grains as the base unit, with 480 grains making up a single troy ounce, about 31.1 grams. That system helped standardize trade and became the weight standard still used for precious metals today.
Some historians think the troy system goes back even further, to ancient Rome. The Romans used bronze bars called aes grave and divided them into 12 units called unciae, or ounces. Each one weighed about 31.1 grams. That close match suggests Roman trade practices likely influenced how Europe later measured precious metals.
The troy system is different than the avoirdupois system most people know.
- 1 grain = 64.8 milligrams (the basic unit)
- 1 pennyweight = 24 grains
- 1 troy ounce = 20 pennyweights = 480 grains = 31.1035 grams
- 1 troy pound = 12 troy ounces = 373.242 grams
Here’s the odd part. A troy ounce is heavier than a regular ounce, but a troy pound is actually lighter than a regular pound. That’s because a troy pound has twelve troy ounces, while a regular pound has sixteen avoirdupois ounces. That difference makes the two systems feel backwards and still catches people off guard.
The troy ounce standard in bullion markets
Today, precious metals are measured using the troy ounce everywhere. It doesn’t matter if you’re buying gold in New York, silver in London, or platinum in Zurich. The same system applies. The market needed one standard so buyers and sellers could trust the weights and avoid confusion or fraud across countries.
U.S. Mint adoption
The U.S. Mint officially adopted the British Imperial Troy ounce in 1828 as the standard for American precious metals. Today, groups like the London Bullion Market Association still use the same system. So when gold is listed at around $4,350 an ounce in early 2026, everyone knows that means $4,350 per troy ounce.
The bullion market needs this kind of accuracy. A large “Good Delivery” bar weighs about 400 troy ounces, or around 12.4 kilograms. At today’s gold prices, that is more than $1.7 million. When that much money is involved, even a tiny weight difference can change the price by thousands of dollars.
Troy ounce vs ounce (metric system)
You encounter the metric system avoirdupois ounce constantly in daily life. It’s the standard unit of measurement for everyday items in the United States, from weighing groceries and cooking ingredients to measuring body weight and shipping packages.
All legitimate precious metal products, including bullion bars, coins, rounds, and jewelry-grade gold or silver, are measured and priced using troy weight exclusively. There are no exceptions to this rule in the legitimate bullion market.
Conversions when weighing precious metals
Even though precious metals always use troy ounces, you’ll sometimes need to switch between systems. For example, this comes up when you compare troy ounces to grams. Here’s how to convert:
| From | To | Conversion factor | Example |
|---|---|---|---|
| Troy ounces | Grams | Multiply by 31.1035 | 5 troy oz = 155.52 g |
| Grams | Troy ounces | Divide by 31.1035 | 100 g = 3.215 troy oz |
| Troy ounces | Avoirdupois ounces | Multiply by 1.09714 | 10 troy oz = 10.97 avdp oz |
| Avoirdupois ounces | Troy ounces | Multiply by 0.91146 | 10 avdp oz = 9.11 troy oz |
| Troy ounces | Pennyweights | Multiply by 20 | 1 troy oz = 20 dwt |
| Grains | Grams | Multiply by 0.0648 | 480 grains = 31.1 g |
Protecting yourself in the global market
The difference between troy and regular ounces can cause expensive mistakes. Imagine you see an ad for “1-ounce gold bars” but it doesn’t say troy ounce. If you assume it means a regular ounce, you’ll be off by almost 10% on the actual weight.
It can also work the other way. If a price looks unusually cheap, the seller might be using regular ounces when precious metals should be priced in troy ounces. Sometimes that’s just confusion, but sometimes it’s a scam. Knowing the difference helps you spot red flags before you lose money.
Common weight-related mistakes:
- Assuming “ounce” always means troy ounce without verification
- Confusing gram weights with troy ounce weights when comparing products
- Failing to account for the weight difference when calculating total investment value
- Using kitchen scales (calibrated in avoirdupois) to verify precious metal products
- Not asking explicitly which measurement system is being used in transactions
Always check that precious metals are listed in troy ounces. Reputable dealers will clearly say “troy ounce” or use “ozt.” If it just says “oz,” ask which system they’re using. When something looks off, do the conversion yourself to confirm the weight and price.
Learn more with Swiss America
Now that you know the difference between a troy ounce and a regular ounce, you can make smarter buying decisions. You don’t need to get lost in industry language. What matters is knowing exactly what you’re paying for.
Swiss America uses the troy ounce standard for all gold, silver, bullion, and IRA-eligible metals, so there’s no confusion about weight or value. To learn more about investing in gold and silver, connect with the Swiss America team today!
Troy oz vs ounce: FAQs
Why is a pound of gold only 12 ounces?
Gold, silver, platinum, and palladium metals use the troy system. In that system, one troy pound equals 12 troy ounces, with each ounce weighing about 31.1 grams, for a total of roughly 373 grams. A regular pound works differently. It has 16 ounces and weighs about 454 grams.
- Troy weight system: Developed for trading valuable goods like precious metals and spices.
- Avoirdupois pound: Designed for everyday goods like food, cloth, and tools, which is why it uses 16 smaller ounces instead of 12 larger ones.
- Precious metals: Today, the troy ounce is the measurement for precious metals worldwide.
Does the IRS know if you buy gold and silver?
No. The IRS does not automatically know about every gold, silver, and platinum purchase. Dealers only report transactions in certain situations, like:
- Over $10,000: Cash payments over $10,000 require Form 8300, and specific large sales of qualifying bullion back to a dealer, which can trigger Form 1099-B.
- Under $10,000: If you buy with a check, wire, card, or cash under the reporting limit, the dealer does not report it. Many common items, like American Gold Eagles, also do not fall under reporting rules for sales.
- Taxes: If you sell at a profit, you’ll report capital gains when you file your return, using Schedule D.
Is it legal to own a 40 oz gold bar?
There’s no federal limit on how much gold you can own. The U.S. removed ownership restrictions in 1975, so you can legally own any amount of gold bullion, including large 40 troy ounce bars. There are no caps on size or quantity for personal ownership. A few things to note:
- Reporting rules: Large cash purchases do trigger reporting rules. If you buy more than $10,000 in cash, the dealer must file a report for anti-money laundering purposes.
- Taxes: When you go to sell bullion, any profits may be subject to capital gains tax. Also note, depending on where you live, you also may have sales tax costs.
- Brands: You can find 40 oz gold bars from major refiners like PAMP and Valcambi. These are known as “Good Delivery” bars and are widely traded by investors and institutional buyers.
How does Swiss America protect customers from gold scams?
Swiss America works to protect customers from gold scams by focusing on verified sourcing, secure storage, and strict standards. Dealer safeguards include:
- Longevity: Swiss America has operated as an authorized dealer since 1982.
- Quality metals: The company sells only quality metals. Coins come with verification documents, and bars come with assay certificates.
- Two-way market: The company remains committed to the products it sells and will buy back your metals if you need to sell in the future.
- Education: Swiss America provides guidance on how to spot fake metals, including checking purity and serial numbers.
The information in this post is for informational purposes only and should not be considered tax or legal advice. Please consult with your own tax professionals before making any decisions or taking action based on this information.
