Troy Ounce vs Standard Ounce: the difference
Understand the difference between a Troy Ounce (31.1035g) and a standard avoirdupois ounce (28.3495g) for precious metals trading and weight conversions.
Key facts
- 1 troy ounce
- 31.1035 grams
- 1 avoirdupois ounce
- 28.3495 grams
- Difference %
- +9.72% (troy > avoirdupois)
- 1 tola (South Asia)
- 11.6638 grams
- 1 grain (troy)
- 0.0648 gram
- Standard in precious metals
- Troy ounce (LBMA, COMEX)
At a glanceIn precious metals trading and global financial markets, the term ounce frequently causes confusion for novice buyers. There are two distinct units sharing the same name: the troy ounce (oz t), used exclusively for gold, silver, platinum, and palladium, and the avoirdupois ounce (oz), used for everyday goods in the English-speaking world. This guide explains mathematical conversions, history, and commercial traps.
Key Figures: 31.1035 g vs. 28.3495 g
The difference is significant:
- 1 Troy Ounce (oz t) = 31.1034768 grams (rounded to 31.1035 g).
- 1 Avoirdupois Ounce (oz) = 28.3495231 grams (rounded to 28.35 g).
A troy ounce is exactly 9.715% heavier than a standard commercial ounce!
When gold trades at 2,900 USD on the LBMA or COMEX, that quotation applies strictly to one troy ounce of 31.1035 grams of fine gold, not an everyday ounce.
Historical Origin: The Fairs of Troyes
The troy ounce is named after the French town of Troyes in Champagne. In the 12th and 13th centuries, the Troyes trade fairs were western Europe's commercial center. Merchants developed a precision weight system based on barley grains:
- 1 troy ounce equaled exactly 480 grains.
- 1 troy pound equaled 12 troy ounces (373.24 g).
In 1527, King Henry VIII officially adopted the troy ounce for the British Royal Mint, standardizing international bullion trading.
Global Precious Metal Weight Conversion Table
| Unit of Measurement | Symbol | Trading Region / Market | Exact Weight in Grams | Equivalent in Troy Ounces (oz t) | Equivalent in Grains |
|---|---|---|---|---|---|
| Troy Ounce | oz t | Global bullion market (LBMA) | 31.1035 g | 1.0000 oz t | 480 grains |
| Avoirdupois Ounce | oz | Food / UK & US commercial trade | 28.3495 g | 0.9115 oz t | 437.5 grains |
| Pennyweight | dwt | Anglo-Saxon jewelry trade | 1.5552 g | 0.0500 oz t (1/20 oz t) | 24 grains |
| Tola | tola | India, Pakistan, Dubai | 11.6638 g | 0.3750 oz t (3/8 oz t) | 180 grains |
| Tael (Hong Kong) | tael | China, Singapore | 37.4290 g | 1.2033 oz t | 577.6 grains |
| Gold Baht | baht | Thailand (96.5% purity) | 15.2440 g | 0.4901 oz t | 235.2 grains |
| Gram | g | Metric system (Switzerland / EU) | 1.0000 g | 0.03215 oz t | 15.432 grains |
| Kilogram (Bar) | kg | Central banks / 1 kg bars | 1,000.00 g | 32.1507 oz t | 15,432 grains |
Online Counterfeit Pitfall
On online auction sites, unscrupulous sellers sometimes market '1 ounce gold bars' at prices below spot:
- The bar delivered weighs 28.35 g (avoirdupois) rather than 31.10 g (troy).
- You lose 2.754 grams of pure gold—a deficit of over CHF 230 to 260 per ounce purchased!
- Always verify the invoice and assay card explicitly state '1 oz troy' or '31.10 g'.
Frequently Asked Questions (FAQ): Troy Ounces
Why does an ounce of silver cost less than an ounce of gold?
The troy ounce is purely a mass measurement (31.1035 g). Pricing reflects the market value of the respective metal.
How much does a 1 oz Krugerrand weigh compared to a Maple Leaf?
- The Canadian Maple Leaf (999.9 fine gold) weighs exactly 31.10 g.
- The South African Krugerrand (22k / 916.7‰) weighs 33.93 g gross to contain exactly 31.10 g of pure fine gold.
Buy Investment Gold in Switzerland (VAT-Exempt)
Buy and store physical gold in secure Zurich or Geneva vaults at direct live LBMA spot rates.