A troy ounce is about 10% heavier than the ounce on your kitchen scale. Twenty-four karat gold is not chemically pure. A "400 ounce" Good Delivery bar is usually not 400 ounces. And the tola, the baht and the tael are all still in daily commercial use in markets that buy more gold than the West does.
None of this is trivia. Every one of those quirks is a place where a buyer can be confused, a comparison can be made wrong, or a price can be quoted in a unit the buyer did not expect. This is the reference article for the vocabulary, written so that you can read a bar stamp, a dealer quote and a token's backing disclosure without having to guess.
The troy system descends from the medieval trade fairs of Troyes in France and survived into modern precious metals commerce after the avoirdupois system took over general commerce.
One troy ounce is exactly 31.1034768 grams. That is a defined figure, not an approximation.
The confusion is that the ordinary ounce, properly the avoirdupois ounce, is 28.349523125 grams. A troy ounce is roughly 9.7% heavier.
The traps that follow are predictable and common:
Converting with the wrong ounce. If you convert a gram figure using 28.35, you will understate the value of a gold holding by about 10%.
Assuming a troy pound behaves like a normal pound. It does not. A troy pound is 12 troy ounces, not 16, which makes it lighter than an avoirdupois pound despite the heavier ounce. The troy pound has no role in modern gold trading and exists mainly to confuse people.
Reading a scrap or jewellery quote. Retail jewellery and scrap buying is usually quoted per gram, and the conversion back to a per-ounce comparison is where consumers most often lose track of what they were offered.
The useful conversions, kept in one place:
Fineness expresses gold content in parts per thousand. 999.9 fineness is 99.99% gold, commonly called four nines. 995 is 99.5%. The number is precise and it is what appears on investment bars.
Karat is the traditional jewellery scale, expressing gold content in twenty-fourths. 24 karat is nominally pure, 22 karat is 22 parts gold in 24, and so on.
Two points that trip people up.
24 karat is a nominal category, not a chemical claim. Absolute purity does not exist in commercial production. Refiners produce 999.9 and occasionally 999.99, and both are sold as 24 karat. When a jewellery piece is described as 24K, it is a category statement.
Karat does not describe weight. A 14 karat chain weighing 20 grams contains about 11.7 grams of gold. Buying jewellery for gold content and paying per gross gram is how people overpay without noticing.
On any item that is not 999.9 pure, two weights exist.
Gross weight is the total weight of the object.
Fine weight is the weight of the gold in it, which is gross weight multiplied by fineness.
A Good Delivery bar with a gross weight of 402.317 troy ounces at 996.5 fineness contains 400.909 troy ounces of fine gold. That fine weight is the number on the bar list, the number in the accounting, and the number the market is paying for. Any bar list worth reading records all three: gross weight, fineness, and fine weight.
When you look at a reserve attestation or a token's backing disclosure, this is what you should expect to see. A disclosure that states only a total in "bars" or a rounded tonnage without fine weights is a weaker document than one with per-bar detail. The checking procedure is in How to Verify Gold Token Reserves Yourself.
LBMA Good Delivery (large bar). The wholesale standard. Must contain between 350 and 430 troy ounces of fine gold, minimum fineness 995, produced by an accredited refiner on the Good Delivery List, and marked with the refiner's stamp, a serial number, the fineness and the year of manufacture. Because the acceptable range is wide, each bar's weight is individual and recorded, which is why they are traded by fine weight rather than by count.
Commonly called "400 ounce bars," which is a convenient shorthand for a range.
Kilobar. One kilogram, typically 999.9 fineness. The dominant form in Asian markets and the reason Swiss refineries do so much recasting. A kilobar is 32.1507 troy ounces.
Retail bars. 1 gram through 100 grams, and 1 troy ounce, typically 999.9. Fabrication cost per gram rises steeply as size falls, which is the economics behind the premiums discussed in Gold Coins vs Bars.
Bullion coins. Usually one troy ounce of fine gold. Fineness varies by programme: some are 999.9 fine, and others, notably the Krugerrand and the American Gold Eagle, are alloyed for durability, which means the coin's gross weight exceeds one ounce while containing exactly one troy ounce of fine gold. This is a classic source of confusion and is entirely intentional in the coin's design.
The reason those large bars keep moving through Switzerland to become kilobars is explained in Where Is the World's Gold Stored.
A legitimate investment bar carries a consistent set of markings. Knowing what to look for takes thirty seconds and rules out a great deal.
For small bars, many refiners now ship in a sealed assay card with a matching serial number. Breaking the seal materially affects resale, because the packaging is part of the chain of custody. That is worth knowing before you open one out of curiosity.
Cross-market comparison. A Mumbai jeweller quoting per tola for 22 karat and a London dealer quoting per troy ounce for 999.9 are quoting the same metal in units that differ by both weight and purity. Comparing them requires converting both.
Fabrication cost is per item, not per ounce. Making a one gram bar costs a meaningful fraction of what making a kilobar costs, and that cost is spread over a thousandth of the metal. Small units carry large percentage premiums for a reason that is real rather than exploitative, though the size of the markup still varies enormously between sellers.
Token denomination. Tokenized gold is typically denominated so that one token represents a fixed quantity of fine gold, most commonly one troy ounce or one gram. Which one changes the numbers on the screen completely without changing anything real. Check the denomination before comparing two products or two prices. The category map is in What Is a Gold Token.
Scrap and second-hand selling. This is where units do real damage to consumers. A buyer quoting per gram on gross weight for karat jewellery is paying for gold content only, and the difference between gross and fine weight on 14 karat is 42% of the metal. Nothing improper is happening. The consumer simply has to do the arithmetic.
What is a troy ounce? A unit of precious metals weight equal to exactly 31.1034768 grams. It is about 9.7% heavier than the standard avoirdupois ounce used for everyday goods.
Why is gold measured in troy ounces? The troy system was the standard for precious metals in medieval European trade and was retained for bullion and coinage after avoirdupois took over general commerce. It persists because contracts, benchmarks and exchange specifications are all written in it.
Is 24 karat gold 100% pure? No. It is a nominal category. Commercially produced investment gold is typically 999.9 fine, which is 99.99% gold. Absolute purity is not achievable at production scale.
How much does a gold bar weigh? It depends on the bar. An LBMA Good Delivery bar contains between 350 and 430 troy ounces of fine gold, commonly around 400. A kilobar is one kilogram, or 32.1507 troy ounces. Retail bars run from one gram upward.
What is the difference between 999 and 999.9 gold? 999 is 99.9% pure and 999.9 is 99.99% pure. Both are sold as investment-grade. The difference is negligible in value terms and can matter for specific industrial uses and for certain market standards.
What does fine weight mean? The weight of pure gold contained in an item, calculated as gross weight multiplied by fineness. It is what you are actually buying and what appears on a bar list.
How many grams are in an ounce of gold? 31.1034768 grams, because gold is quoted in troy ounces. If you use 28.35, you are using the wrong ounce and will be out by roughly 10%.
The units are old, inconsistent and completely entrenched. They are not going to change, so the only defence is knowing them.
Three habits cover almost every situation. Convert everything to grams of fine gold before comparing two offers. Read the fineness, not the karat marketing. And when you look at any document claiming to prove gold exists, expect serial numbers, gross weight, fineness and fine weight, because a document without those four things is a statement rather than evidence.
This article is for informational purposes only and is not financial advice.
| Unit | In grams | In troy ounces |
|---|
| Troy ounce | 31.1034768 | 1 |
| Gram | 1 | 0.0321507 |
| Kilogram | 1,000 | 32.1507 |
| Avoirdupois ounce | 28.349523125 | 0.9114583 |
| Tola (South Asia, common form) | 11.6638 | 0.375 |
| Tael (Hong Kong) | 37.429 | 1.2034 |
| Baht (Thailand, gold weight) | 15.244 | 0.4901 |
| Pennyweight | 1.55517 | 0.05 |
| Karat | Gold content | Approximate fineness | Typical use |
|---|
| 24K | 100% nominal | 999 or 999.9 in practice | Investment bars, Asian jewellery |
| 22K | 91.67% | 916 | Indian and Middle Eastern jewellery |
| 18K | 75% | 750 | Western fine jewellery |
| 14K | 58.3% | 585 | Mass market jewellery, US common |
| 9K | 37.5% | 375 | UK entry-level jewellery, legally saleable as gold |
