Key Takeaways
- A troy ounce is exactly 31.1034768 grams. It is the unit used to price gold, silver, platinum and palladium around the world.
- It is heavier than an ordinary ounce: the everyday (avoirdupois) ounce is 28.35 grams, so a troy ounce is about 9.7% heavier.
- But a troy pound is lighter than an ordinary pound: it has only 12 ounces (373.24 g) against 16 ounces (453.59 g).
- The UK still allows it in law for one purpose: under the Weights and Measures Act 1985, the ounce troy may be used for trade in gold, silver and other precious metals.
- One kilogram equals 32.1507 troy ounces, the conversion factor used in the London bullion market.
- On 3 October 2026, one troy ounce of gold was worth £3,135.89 at the spot price, or £100.82 per gram.
A troy ounce is the unit of weight for precious metals. When you see a gold price of “£3,135.89 per ounce” on a chart or a dealer’s site, that ounce is always a troy ounce, never the ounce you use in the kitchen. The difference is small on paper, but it changes how much metal you get for your money.
In this guide, we explain what a troy ounce is, how much it weighs in grams, where the name comes from, how it differs from an ordinary ounce, and how to convert it. You will find conversion tables, current UK spot values from our gold price chart, and an FAQ at the end.
What Is a Troy Ounce?
A troy ounce (symbol oz t, or simply oz in the bullion trade) is a unit of mass equal to exactly 31.1034768 grams. It belongs to the troy weight system, an old system of weights kept today almost exclusively for precious metals. In other words, it is the standard unit of measurement for the weight of precious metals, and it is not the same as the standard ounce you use in a recipe.
Here is the short version of the troy system:
- 1 troy ounce = 31.1034768 grams
- 1 troy ounce = 480 grains
- 1 troy ounce = 20 pennyweights (dwt)
- 1 troy pound = 12 troy ounces = 373.2417 grams
Who uses it today? Almost everyone in the bullion market. The London Bullion Market Association (LBMA) quotes gold and silver prices per troy ounce, mints state the weight of their coins in troy ounces, and dealers list a 1 oz Britannia or a 1 oz gold bar by the same unit.
How much does a troy ounce weigh?
A troy ounce weighs exactly 31.1034768 grams. Both The Royal Mint and the LBMA give this figure. In everyday use, people round it to 31.1 grams, and many dealers use 31.103 grams.
Why exactly that number? The troy ounce is defined as 480 grains, and the grain is defined as 1/7,000 of the international avoirdupois pound. Since 1959, that pound has been fixed at 0.45359237 kilograms, which makes one grain 0.06479891 grams and one troy ounce 31.1034768 grams.
Is the troy ounce legal in the UK?
Yes, but only for precious metals. The Weights and Measures Act 1985 lists the ounce troy among units that may not be used for trade, “except for the purposes of transactions in, or in articles made from, gold, silver or other precious metals”. So a UK dealer can sell you a 1 oz gold coin by troy weight, but a greengrocer cannot sell you apples by the troy ounce.
Troy Ounce vs Ordinary Ounce: What’s the Difference?
The ordinary ounce used for food, post and most goods is the avoirdupois ounce, sometimes called the regular ounce or everyday ounce. It weighs 28.349523125 grams. The troy ounce weighs 31.1034768 grams. That makes the troy ounce about 9.7% heavier than one ounce on a kitchen scale.
Does that mean everything troy is heavier? No, and this is where many people get confused. The troy pound has 12 ounces, while the avoirdupois pound has 16. So a troy pound (373.24 g) is lighter than an ordinary pound (453.59 g).
Why does the difference matter when buying gold?
Because the price is per troy ounce. If you mistakenly value an avoirdupois ounce of gold at the troy ounce price, you overvalue it by about 9.7%. At the spot price on 3 October 2026, that error is worth about £278 per ounce of gold.
It also works the other way. A “1 oz” item weighed on a kitchen scale will show about 31.1 grams, not 28.35 grams. If a coin sold as 1 oz gold weighs 28 grams, something is wrong. Our guide on how to spot fake gold and silver coins explains how weight checks help you catch counterfeits.
Troy vs avoirdupois at a glance
| Unit | Troy system | Avoirdupois system |
|---|---|---|
| Ounce in grams | 31.1034768 g | 28.349523125 g |
| Ounce in grains | 480 grains | 437.5 grains |
| Ounces per pound | 12 | 16 |
| Pound in grams | 373.2417 g | 453.59237 g |
| Used for | Gold, silver, platinum, palladium | Food, post, most everyday goods |
| 1 ounce in the other unit | 1.0971 avoirdupois oz | 0.9115 troy oz |
Read also: Gold Bars vs Gold Coins: Pros and Cons
The History of the Troy Ounce
Where does the name come from? It is usually linked to Troyes, a market town in the Champagne region of north-eastern France. Troyes hosted one of the great trade fairs of medieval Europe, and merchants from many countries needed weights they could all agree on. The LBMA describes the troy ounce as “usually considered” to be named after the weights used at the Troyes fair, so the link is likely but not proven.
Troy weight in England
According to the LBMA, the troy ounce and its relatives, the grain and the pennyweight, have been used for weighing precious metals in England since the 12th century or earlier. For a long time, though, the Royal Mint worked with a different pound, the Tower pound.
That changed in 1527, under Henry VIII. The LBMA notes that the basis of the country’s weights for gold and silver then moved from the “towre” pound to the troy pound of 12 troy ounces. From then on, English coinage was weighed in troy units.
Two centuries later, troy weight was still the language of the Mint. In his 1717 report on the coinage, Sir Isaac Newton, then Master of the Royal Mint, described the guinea in troy terms:
“I humbly represent to Your Lordships, that a Pound Weight Troy of Gold Eleven Ounces fine & one Ounce allay, is cut into 44½ Guineas”
Sir Isaac Newton, Master of the Royal Mint, report to the Lords Commissioners of the Treasury, September 1717
In plain words, one troy pound of 22 carat gold (11 parts gold, 1 part alloy) was struck into 44½ guineas.
From imperial unit to bullion standard
England kept two weight systems side by side. For everyday goods, it used avoirdupois weights for centuries, and the UK later moved to the metric system. The troy ounce survived in one niche: precious metals. Today, it is the unit of the global bullion market from London and Zurich to New York and Perth.
A few milestones:
- 12th century or earlier: troy units used for precious metals in England (LBMA).
- 1527: troy pound replaces the Tower pound as the basis for gold and silver weights in England.
- 1959: under the International Yard and Pound Agreement, the international pound is fixed at 0.45359237 kg, which fixes the troy ounce at exactly 31.1034768 g.
- 1985: the Weights and Measures Act keeps the ounce troy legal for UK trade in precious metals only.
Troy Ounce Conversion Table
The tables below cover the conversions bullion buyers ask about most. The troy ounce to grams conversion is simple:
Grams = troy ounces × 31.1035
Troy ounces = grams ÷ 31.1035
Troy ounces to grams
| Troy ounces | Grams | Kilograms | Value in gold at spot |
|---|---|---|---|
| 1/10 oz | 3.110 g | 0.0031 kg | £313.59 |
| 1/4 oz | 7.776 g | 0.0078 kg | £783.97 |
| 1/2 oz | 15.552 g | 0.0156 kg | £1,567.94 |
| 1 oz | 31.103 g | 0.0311 kg | £3,135.89 |
| 2 oz | 62.207 g | 0.0622 kg | £6,271.78 |
| 5 oz | 155.517 g | 0.1555 kg | £15,679.45 |
| 10 oz | 311.035 g | 0.3110 kg | £31,358.90 |
| 50 oz | 1,555.174 g | 1.5552 kg | £156,794.50 |
| 100 oz | 3,110.348 g | 3.1103 kg | £313,589.00 |
| 400 oz | 12,441.391 g | 12.4414 kg | £1,254,356.00 |
Grams to troy ounces
Gold bars are often sold in grams, so it helps to know how many troy ounces you are buying. A 100 g bar, for example, is just over 3.2 ounces.
| Grams | Troy ounces | Value in gold at spot |
|---|---|---|
| 1 g | 0.0322 oz | £100.82 |
| 2.5 g | 0.0804 oz | £252.05 |
| 5 g | 0.1608 oz | £504.11 |
| 10 g | 0.3215 oz | £1,008.21 |
| 20 g | 0.6430 oz | £2,016.42 |
| 50 g | 1.6075 oz | £5,041.06 |
| 100 g | 3.2151 oz | £10,082.12 |
| 250 g | 8.0377 oz | £25,205.30 |
| 500 g | 16.0754 oz | £50,410.60 |
| 1 kg | 32.1507 oz | £100,821.20 |
You can check these weights against live prices on our pages for the gold price per gram and the gold price per kilogram.
Other troy units: grains and pennyweights
You will meet two smaller troy units, mostly in jewellery and older documents:
- Grain: 0.0648 grams. There are 480 grains in a troy ounce.
- Pennyweight (dwt): 24 grains, or 1.5552 grams. There are 20 pennyweights in a troy ounce.
Scrap gold buyers in some countries still quote prices per pennyweight. In the UK, scrap and bullion prices are usually given per gram or per troy ounce.
How Precious Metal Prices Use the Troy Ounce
The spot price of every major precious metal is quoted per troy ounce. To get a price per gram, divide by 31.1035. To get a price per kilogram, multiply the per gram price by 1,000.
| Metal | Per troy ounce | Per gram | Per kilogram |
|---|---|---|---|
| Gold | £3,135.89 | £100.82 | £100,821 |
| Silver | £45.82 | £1.47 | £1,473 |
| Platinum | £1,287.88 | £41.41 | £41,406 |
| Palladium | £902.50 | £29.02 | £29,016 |
Live prices for each metal are on our silver price, platinum price and gold price charts.
The gold price per troy ounce over the past year
How much has one troy ounce of gold cost in pounds over the last 12 months? It rose from £2,874 on 1 October 2025 to £3,918 on 1 March 2026, the highest of the monthly readings, then eased to £3,136 by 3 October 2026.
Troy Ounces in the Bullion You Buy
Most bullion products are made to a round number of troy ounces or grams. Knowing the fine weight (the weight of pure metal) helps you compare prices fairly.
| Product | Fine metal content | In grams |
|---|---|---|
| Gold Britannia 1 oz (The Royal Mint) | 1 troy oz gold | 31.10 g |
| Gold Sovereign (The Royal Mint) | 0.2354 troy oz gold | 7.32 g (total weight 7.98 g, 22 carat) |
| 1 oz gold bar | 1 troy oz gold | 31.10 g |
| 1 kg gold bar | 32.15 troy oz gold | 1,000 g |
| LBMA Good Delivery gold bar | approximately 400 troy oz | about 12.4 kg |
| LBMA Good Delivery silver bar | approximately 1,000 troy oz | about 31.1 kg |
Why does the Sovereign weigh 7.98 grams but contain only 7.32 grams of gold? It is 22 carat gold, an alloy of 91.67% gold with copper for hardness. When you compare a Sovereign with a 1 oz coin, always use the fine gold content, not the total weight.
Read also: Large or Small Denominations: What’s Better When Buying Gold?
How to compare prices per troy ounce
Different sizes carry different premiums over spot. To compare them, follow these steps:
- Find the fine weight of the product in troy ounces (for example, 100 g = 3.2151 oz).
- Divide the dealer’s price by that number to get the price per troy ounce.
- Compare the result with the spot price per troy ounce.
The gap between the two is the premium. The same method works whether you buy gold or are selling gold back to a dealer, because a refinery stamps the fine weight and purity on its bars. You can see how premiums compare across UK dealers in our categories for 1 oz gold bars, Britannia gold coins and 1 kg gold bars.
Read also: LBMA: All You Need to Know
Summary: Troy Ounce
| Question | Answer |
|---|---|
| Weight of one troy ounce | 31.1034768 g (exact) |
| Troy vs ordinary ounce | About 9.7% heavier (31.10 g vs 28.35 g) |
| Troy pound | 12 troy ounces, 373.24 g |
| Troy ounces in 1 kg | 32.1507 |
| Used for | Gold, silver, platinum and palladium prices and bullion weights |
| UK legal status | Allowed for trade in precious metals (Weights and Measures Act 1985) |
FAQ: Troy Ounce
How many grams are in a troy ounce?
There are exactly 31.1034768 grams in a troy ounce. Most dealers round this to 31.1 g or 31.103 g.
Is a troy ounce the same as an ounce?
No, a troy ounce (31.10 g) is about 9.7% heavier than an ordinary avoirdupois ounce (28.35 g). Precious metal prices always refer to the troy ounce.
Which is heavier, 1 oz or 1 troy ounce?
One troy ounce is heavier than one ordinary ounce. The difference is 2.75 grams per ounce.
Why is it called a troy ounce?
The name is usually linked to Troyes, a French market town with major medieval trade fairs. The LBMA says it is “usually considered” to come from there, so the origin is likely but not certain.
How many troy ounces are in a kilogram?
There are 32.1507 troy ounces in a kilogram. A 1 kg gold bar therefore contains about 32.15 troy ounces of pure gold.
How many troy ounces are in a kilo of silver?
A kilo of silver also contains 32.1507 troy ounces, because the troy ounce measures weight, not the metal. A 1 kg silver bar of 999 fineness holds just over 32 troy ounces of fine silver.
What is a troy ounce of gold worth today?
On 3 October 2026, one troy ounce of gold was worth £3,135.89 at the spot price. Check the live price on our gold price chart before you buy or sell.
How many troy ounces are in a troy pound?
There are 12 troy ounces in a troy pound, which weighs 373.24 grams. An ordinary pound has 16 ounces and weighs 453.59 grams.
Compare Gold Prices per Troy Ounce
Now you know what a troy ounce weighs, you can check whether a price is fair. The spot price tells you the value of the metal. The dealer’s price per troy ounce tells you what you actually pay.
Compare prices for gold coins and gold bars across UK bullion dealers, or follow the live gold price to see how much one troy ounce costs today.
This article is for information only and is not investment or tax advice.
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