Troy Ounce to Grams: The Complete Gold Weight Guide
If you've ever wondered why a gold "ounce" doesn't weigh the same as the ounce on your kitchen scale, you've stumbled into the strange and ancient world of the troy ounce — the unit that has measured precious metals since medieval France. Here's exactly what it is, how to convert it, and why every investor should know the difference.
Walk into any bullion dealer, scroll any precious-metals quote, or read any gold ETF prospectus, and you'll see prices listed per troy ounce — abbreviated oz t or ozt. It is one of the only archaic units to survive into modern global finance, and it's not the same as the ounce on a postal scale. The difference is small, but at gold prices the few extra grams add up quickly.
This guide explains everything: the exact conversion, where the unit came from, how it's used in standard gold bar sizes, and the maths you need to value any quantity of gold accurately. If you are working with ordinary kitchen, shipping or jewellery-display weights instead of troy weights, compare those numbers with the ounces to grams and grams to ounces converters before applying the gold formula.
Troy ounce, gram & kilogram converter
Convert instantly between troy ounces, grams, kilograms, and standard ounces.
What is a troy ounce?
A troy ounce is a unit of mass used worldwide for weighing precious metals — gold, silver, platinum and palladium — and gemstones in some markets. It is the standard quoted unit on every major bullion exchange, from the London Bullion Market Association to the COMEX in New York to the Shanghai Gold Exchange.
The troy ounce traces its name to the city of Troyes in northeastern France, which was a major hub for international trade fairs during the Middle Ages. The system of weights used at these fairs eventually became standardised across Europe and was formally adopted by Britain in 1527 under King Henry VIII for measuring precious metals. The system has barely changed in five centuries.
1 troy ounce = 31.1034768 grams — exactly. This is the figure quoted on every gold price ticker in the world.
Troy ounce vs standard ounce
This is the most common point of confusion in precious-metals trading. The "ounce" you weigh food with is the avoirdupois ounce — French for "goods of weight". It's not the same as the troy ounce, and assuming they are will cost you about 10% on every transaction.
Troy ounce (oz t)
31.1035 g- Used for: gold, silver, platinum, palladium
- Dates from medieval Troyes, France
- 1 troy lb = 12 troy oz (note: not 16)
- Symbol: oz t or ozt
Standard ounce (oz)
28.3495 g- Used for: food, postage, body weight
- Avoirdupois system (most everyday use)
- 1 lb = 16 oz
- Symbol: oz
The troy ounce is roughly 10% heavier than the standard ounce. Specifically: 31.1035 ÷ 28.3495 = 1.09714, a difference of about 9.71%. So if a gold dealer quoted you a price for "1 ounce" without specifying troy, and you assumed they meant a regular ounce, you'd be missing nearly 3 grams of gold.
For non-precious-metal weights, the everyday ounce still follows the standard pound system: use ounces to pounds or pounds to ounces for grocery, postage and body-weight figures, but keep those separate from troy ounces.
The exact conversion
For everyday calculations, two formulas cover everything:
Troy ounce to grams chart
Reference table for the values that come up most often in bullion trading and jewellery:
| Troy ounces | Grams | Standard ounces |
|---|---|---|
| 0.10 oz t | 3.11 g | 0.110 oz |
| 0.25 oz t | 7.78 g | 0.274 oz |
| 0.50 oz t | 15.55 g | 0.548 oz |
| 1 oz t | 31.10 g | 1.097 oz |
| 2 oz t | 62.21 g | 2.194 oz |
| 5 oz t | 155.52 g | 5.486 oz |
| 10 oz t | 311.03 g | 10.971 oz |
| 20 oz t | 622.07 g | 21.943 oz |
| 50 oz t | 1,555.17 g | 54.857 oz |
| 100 oz t | 3,110.35 g | 109.714 oz |
Standard gold bar weights
Gold is sold in standardised sizes that hop between metric (grams, kilograms) and troy ounces depending on where in the world you are. Here are the sizes you'll actually encounter:
Metric bar listings often show the same product in grams and kilos. For those labels, the simple grams to kilograms and kilograms to grams conversions are enough before you translate the result into troy ounces.
The 400-troy-ounce gold bar — about 12.4 kg — is the standard "Good Delivery" bar accepted by central banks and the London Bullion Market. These are the bars you see in vault photos, and each one is currently worth well over a million US dollars at typical gold prices.
How many troy ounces in a kilogram?
For larger weights, the kilogram is the working unit — particularly for kilo bars and central-bank reserves.
When holdings move beyond single bars, reports may switch between kilograms and tonnes. In that case, kilograms to tonnes and tonnes to kilograms are the clean metric conversions to use before calculating troy ounces.
| Kilograms | Troy ounces | Approximate value* |
|---|---|---|
| 0.1 kg | 3.22 oz t | ~$10,000 |
| 0.5 kg | 16.08 oz t | ~$50,000 |
| 1 kg | 32.15 oz t | ~$100,000 |
| 2 kg | 64.30 oz t | ~$200,000 |
| 5 kg | 160.75 oz t | ~$500,000 |
| 10 kg | 321.51 oz t | ~$1,000,000 |
| 12.4 kg | ~400 oz t | ~$1,250,000 (Good Delivery) |
*Indicative gold values at roughly $3,100/oz t — actual prices fluctuate constantly.
Purity, karats and weight
One trap that catches new investors: a "1 oz gold ring" rarely contains 1 troy ounce of pure gold. That's because most jewellery isn't pure — it's an alloy. The karat system measures purity, not weight, and is a separate concept from the troy ounce, which measures total mass.
| Karat | Purity | Pure gold in 1 oz t (31.10 g) |
|---|---|---|
| 24K | 99.9% (pure) | 31.07 g of gold |
| 22K | 91.7% | 28.51 g of gold |
| 18K | 75.0% | 23.33 g of gold |
| 14K | 58.3% | 18.13 g of gold |
| 10K | 41.7% | 12.97 g of gold |
| 9K | 37.5% | 11.66 g of gold |
"Karat" (with a K) describes gold purity. "Carat" (with a C) describes the weight of gemstones (1 carat = 0.2 g). They sound the same and are easily confused — use carats to grams or grams to carats for gemstone weight. For a fuller explanation, see our Carat Guide.
Calculating the value of gold
Once you can convert between troy ounces and grams, valuing any piece of gold becomes simple arithmetic. The formula:
This calculates the melt value — the worth of the gold itself. Finished jewellery sells for far more (because of design, brand and craftsmanship), and dealers will buy below melt value to make a profit on resale.
Scrap lots are sometimes weighed on ordinary scales before the gold content is priced. If the weight is listed in pounds, convert pounds to grams or grams to pounds first, then divide the gram figure by 31.1035 to get troy ounces.
A brief history of the troy ounce
The troy weight system traces back to medieval Europe — most likely to the trade fairs held in Troyes, in the Champagne region of France, during the 12th and 13th centuries. Merchants from across the continent gathered there to trade goods, and a standardised system of weights was essential for honest dealing in valuable items like silver, gold, gunpowder and gemstones.
England formally adopted troy weights for precious metals in 1527, replacing the older "tower pound" used at the Royal Mint. The United States followed in 1828, mandating troy weights for the federal coinage system. Despite the metric revolution that swept through most of science and commerce in the 19th and 20th centuries, the precious-metals industry never moved on — partly because of inertia, partly because every long-running price chart, contract and historical record is denominated in troy ounces.
One curious detail: the troy pound contains 12 troy ounces, not 16. The troy pound itself is now obsolete (it was abolished in the UK in 1878), but its legacy is why gold and silver "pounds" don't behave like grocery pounds.
In modern logistics and vault accounting, the opposite problem is more common: bulk metal can appear as kilos, standard pounds, or tonnes. To keep those records straight, convert pounds to kilograms, kilograms to pounds, or tonnes to pounds separately from any troy-ounce calculation.
Mistakes that cost investors money
- Confusing oz with oz t. A 1 oz t gold coin contains about 9.7% more gold than a "1 oz" weight on a kitchen scale. Always check whether a quote is troy.
- Buying by gross weight, ignoring purity. A 22K coin weighing 1 oz t contains only ~28.5 g of pure gold, not 31.1 g. The remaining 8% is alloy (usually copper or silver) for hardness.
- Mixing karats and carats. Karats measure gold purity; carats measure gemstone weight. They are unrelated despite the near-identical spelling.
- Comparing prices in different currencies without checking the unit. Some markets (notably the Middle East) sometimes quote in grams instead of troy ounces — make sure you're comparing like with like.
- Forgetting the spread. Dealers buy below the spot price and sell above it. A "premium-free" 1 oz gold coin is usually a marketing fiction — there's always some markup.
Conversion tools
Note: our standard converters use the avoirdupois ounce. To convert troy ounces, use the calculator at the top of this page or multiply by 31.1035 manually.