Quick answer
A troy ounce is 31.1034768 grams, the international unit gold, silver, platinum, and palladium are priced and settled in.
The troy ounce is roughly 9.7 percent heavier than the everyday avoirdupois ounce printed on cereal boxes. Every spot price quoted on a major benchmark, every headline reading “gold at $3,300 an ounce,” and every bullion coin specification from the U.S. Mint uses the troy ounce as the reference. Confusing the two units at a jewelry counter costs a seller about one dollar for every ten owed.
The definition, to eight decimal places
One troy ounce equals 31.1034768 grams. Exact. Not rounded. The number comes from the international agreement on customary units signed in 1959 by the United States, the United Kingdom, Canada, Australia, and other members of the yard-and-pound treaty, which defined the grain as exactly 64.79891 milligrams. From that grain, every troy unit follows: 24 grains to a pennyweight, 20 pennyweights to a troy ounce, 12 troy ounces to a troy pound.
Commercial scales sold in the United States must display troy weight when used in precious metals commerce. The rule is codified in NIST Handbook 44, the federal specification every state weights-and-measures inspector enforces at the counter. Scales that display only avoirdupois or metric units are not legal for gold and silver transactions unless the buyer converts every quote in writing.
Troy versus avoirdupois: the table every seller should keep
The avoirdupois ounce is the one on your bathroom scale, on grocery packaging, and on the U.S. Postal Service rate schedule. It is 28.349523125 grams exactly. The troy ounce is 2.75 grams heavier. That is a small absolute difference, but on a full ounce of gold at $3,300 spot, it is about $290 of metal.
| Unit | Grams | Used for |
|---|---|---|
| 1 troy ounce (ozt) | 31.1034768 g | Gold, silver, platinum, palladium (bullion, jewelry, coins) |
| 1 avoirdupois ounce (oz) | 28.349523125 g | Everyday retail, groceries, postal weight |
| 1 troy pound | 373.2417216 g | Precious metals; equals 12 troy ounces |
| 1 avoirdupois pound | 453.59237 g | Everyday retail; equals 16 avoirdupois ounces |
| 1 pennyweight (dwt) | 1.5551738 g | American jewelry and dental gold pricing |
| 1 grain | 0.06479891 g | Historical unit; still used for firearms |
Note the odd inversion. A troy pound is lighter than an avoirdupois pound (373 g versus 454 g), because a troy pound contains only 12 ounces to the avoirdupois 16. But the troy ounce is heavier than the avoirdupois ounce. Two centuries of merchants have tripped on that distinction. It is the reason older estate paperwork sometimes lists gold in “pounds” without specifying which system, leaving heirs to reconcile the difference decades later.
Where the troy ounce came from
The unit takes its name from the medieval French city of Troyes, a market town in the Champagne region roughly 100 miles southeast of Paris. Troyes hosted one of Europe’s largest annual trade fairs from the 12th through the 14th century. Merchants from Genoa, Flanders, and the Baltic settled accounts in a standardized weight system that eventually took the city’s name.
England adopted the troy system for gold and silver by royal decree under Henry VIII in 1527, replacing the older tower pound of the London mint. The United States Mint, founded in 1792, chose the troy ounce for its precious metals operations from the start. Britain formally banned the troy pound for most trade in 1878, but kept the troy ounce for bullion, and every major refiner and exchange followed suit.
The system survived because it was already the language of every serious metals contract. Assay offices, refineries, mints, and settlement banks had built their books on it. When the London Bullion Market Association codified the modern spot market after 1919, it kept the troy ounce as the settlement unit for the twice-daily gold fix. It has not moved since.
Why precious metals still price in troy ounces
Three practical reasons. First, market continuity. Switching the settlement unit on a market that clears trillions of dollars annually would require re-papering every futures contract, ETF prospectus, mining reserve report, and central bank balance sheet. The friction dwarfs any convenience gain.
Second, precision at scale. A pennyweight (one-twentieth of a troy ounce) is a coarse enough increment for a jeweler to weigh a chain by hand, and the troy ounce is a fine enough increment for a refinery to weigh a 400-ounce Good Delivery bar. The system nests cleanly from grain to pound with whole-number ratios that avoid rounding drift over long ledgers.
Third, fraud resistance in the retail channel. Because “troy ounce” is a legally-required label on precious metals scales, a dealer who quotes “per ounce” without the qualifier is signaling either ignorance or a setup. The unit itself functions as a compliance flag. The Federal Trade Commission reminds consumers that reputable jewelry and bullion transactions always disclose weight in troy units, purity in karat or fineness, and the spot reference used for pricing.
Common mistakes when weighing jewelry at home
Most Americans who weigh a chain or a set of rings before selling use a small digital pocket scale bought online. The scales are accurate to within a tenth of a gram, but they invite the same handful of mistakes. Any one of them can shift a fair offer by 10 percent or more.
Reading grams and pretending they are troy ounces
A 62-gram chain is not “62 ounces of gold.” It is 1.99 troy ounces of alloy. To convert grams to troy ounces, divide by 31.1034768. To convert grams to pennyweights (the unit most American jewelers quote), divide by 1.5551738. Do the arithmetic before you compare quotes, not during the offer conversation.
Ignoring purity and pricing the alloy as if it were pure gold
A 14-karat piece is 58.3 percent pure gold by weight (0.583 fraction). An 18-karat piece is 75.0 percent. A 22-karat coin is 91.67 percent. Multiply the total weight by the karat fraction to get the pure metal content, then multiply by the spot price per troy ounce. A 40-gram 14K chain contains 23.32 grams (0.7498 troy ounces) of pure gold, worth roughly $2,474 at a $3,300 spot, before any dealer margin or refining fee.
Weighing on a scale set to the wrong unit
Many pocket scales default to grams but can toggle to pennyweights, carats, or “ct” (which sometimes means carats, sometimes grains, depending on the manufacturer). The abbreviations are small on the display and easy to overlook. Always check the unit label before reading the number, and take a photograph of the scale readout with your phone for your records.
Weighing gold set with stones without accounting for them
A ring set with a half-carat diamond contains roughly 0.1 gram of stone (a carat is 0.2 g). On a small ring, that is a measurable slice of the total weight. Reputable buyers deduct stone weight before pricing the metal. If a quote does not, the seller is being paid for stones as though they were gold and will likely be underpaid when the buyer resells the pieces separately.
Comparing quotes in different units without converting
Buyer A pays $61 per gram of 24K. Buyer B pays $95 per pennyweight of 24K. Which offer is higher? Convert both to the same unit before answering. $95 per dwt divided by 1.5551738 g/dwt equals $61.09 per gram. The offers are effectively tied. Buyer C pays $1,900 per troy ounce of 24K, which is $61.09 per gram. Also tied. Any offer meaningfully different is either better, worse, or hiding a discount in the unit.
See every offer in writing before you sell
The simplest defense against unit confusion is to receive every offer in writing, with the buyer’s assumed spot price, purity, and weight unit shown on the same document. Rather than driving from dealer to dealer, submit one free request on Goldiew’s sell gold page and receive sealed bids from up to 15 verified precious metals buyers. Every bid arrives in troy units with the spot and karat explicitly stated. You can also browse the Goldiew marketplace to see what comparable pieces are selling for before you decide on a floor price.
Frequently asked questions
How many grams are in a troy ounce?
Exactly 31.1034768 grams. The value is a defined constant, not a measurement, and comes from the international yard-and-pound agreement of 1959. Every spot price, dealer quote, and bullion coin specification in the United States uses this figure. It is also the settlement unit for the London Bullion Market Association.
Is a troy ounce heavier than a regular ounce?
Yes. A troy ounce weighs 31.1034768 grams. A regular (avoirdupois) ounce weighs 28.349523125 grams. The troy ounce is about 9.7 percent heavier. When a dealer quotes “per ounce” without specifying troy, ask which unit they mean. On a full ounce of gold at a $3,300 spot, the difference is roughly $290 in metal value.
Why is the abbreviation for a troy ounce “ozt” instead of “toz”?
Both abbreviations appear in the wild. “ozt” is the format adopted by the International Bureau of Weights and Measures and by most bullion refiners. “t oz” and “oz t” also show up on some coin certificates and older textbooks. All three refer to the same 31.1034768-gram unit. The regular avoirdupois ounce is simply “oz” with no qualifier.
Do American jewelers use troy ounces or grams?
American jewelers and dental gold buyers most often quote in pennyweights (dwt), an old English unit that equals one-twentieth of a troy ounce, or about 1.55 grams. Bullion dealers use troy ounces. Almost every digital scale defaults to grams. That is three units in circulation at a single counter. For a full conversion reference, see the pennyweight, gram, and troy ounce conversion guide.
Do bullion coins actually weigh one troy ounce?
A “one-ounce” bullion coin contains exactly one troy ounce (31.1034768 g) of the stated precious metal, but the total coin can weigh more. The American Gold Eagle weighs 33.931 grams total; 31.1 grams is pure gold and the balance is copper and silver alloyed in for durability. The American Gold Buffalo, which is 99.99 percent pure, weighs almost exactly 31.1 grams. Every mint publishes total and pure weights side by side.
Where does the troy ounce come from historically?
The unit takes its name from the medieval French trading city of Troyes, which hosted one of Europe’s largest fairs in the 12th to 14th centuries. Henry VIII made troy the standard for English gold and silver in 1527, and the U.S. Mint adopted it in 1792. Britain kept it for bullion when it abolished the troy pound for most trade in 1878. Every major exchange has used it since.
How is a troy ounce different from the IRA-eligible weight standards?
The troy ounce is only a weight unit. IRA eligibility adds a separate requirement on purity: 99.5 percent for gold, 99.9 percent for silver, and 99.95 percent for platinum and palladium, with certain American Eagle coins exempted by statute. A one-ounce American Gold Eagle at 91.67 percent purity is IRA-eligible by name, while a one-ounce 22-karat foreign coin is not. Weight and purity are independent tests. For the retirement-account version of this comparison, see what is a troy ounce vs a regular ounce for precious metals.
Which precious metals are priced in troy ounces?
All four investment-grade precious metals: gold, silver, platinum, and palladium. Rhodium and iridium, which trade in much smaller volumes, are also quoted in troy ounces. Base metals like copper and aluminum are priced in metric tons or avoirdupois pounds instead. If the market quote is in troy ounces, the metal is almost certainly one of the four in the precious basket.
Sources
- NIST Handbook 44: Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices (troy versus avoirdupois definitions, scale marking rules for commercial precious metals transactions)
- NIST: International System of Units (grain, gram, kilogram definitions used for troy conversions)
- London Bullion Market Association: Precious Metal Prices (troy ounce as the global settlement unit for gold, silver, platinum, palladium)
- United States Mint: History (adoption of the troy ounce for U.S. coinage in 1792)
- United States Mint: American Eagle Coin Program (specifications for one-troy-ounce bullion coins, total versus pure weight)
- Federal Trade Commission: Shopping for Jewelry (weight and purity disclosure standards)