What Is a Troy Ounce?
By Alex Capitol · Updated 2026-04-14 · Methodology
A troy ounce is 31.1035 grams — approximately 10% heavier than a regular (avoirdupois) ounce of 28.3495 grams. It is the universal standard for measuring and pricing gold, silver, platinum, and palladium. When you see "gold price per ounce," it always means per troy ounce, not a regular ounce.
Check the live gold price for today's value per troy ounce.
Troy Ounce vs Regular Ounce
| Measurement | Troy Ounce | Regular (Avoirdupois) Ounce |
|---|---|---|
| Weight in grams | 31.1035g | 28.3495g |
| Difference | — | 9.7% lighter |
| Used for | Gold, silver, platinum, palladium | Everything else (food, postage, etc.) |
| Abbreviation | ozt or t oz | oz |
| Per pound | 12 troy oz/troy pound | 16 oz/pound |
| Pound weight | 373.24g (troy pound) | 453.59g (avoirdupois pound) |
Key point: A troy ounce is heavier than a regular ounce, but a troy pound (12 troy ounces = 373g) is lighter than a regular pound (16 ounces = 454g). This confuses many people — the systems aren't proportional.
Why Precious Metals Use Troy Ounces
The troy ounce dates back to medieval Europe, most likely to Troyes, France — a major trading hub in the Middle Ages. The Troyes weight system was standardized for precious metals and gemstones, and it stuck.
Timeline:
- ~1200s — Troyes, France establishes standardized weights for its trade fairs
- 1527 — England officially adopts the troy ounce for gold and silver coinage
- 1828 — US adopts the troy ounce as the legal standard for currency (US Mint Act)
- Today — COMEX, LBMA, and every major precious metals exchange worldwide use troy ounces
The troy ounce persists because the global gold market needs a single, consistent unit. Changing it would require repricing centuries of historical data and rewriting every futures contract. The cost of switching far exceeds any convenience benefit.
Troy Ounce Conversion Table
| From | To | Value |
|---|---|---|
| 1 Troy Ounce | Grams | 31.1035g |
| 1 Troy Ounce | Kilograms | 0.0311035 kg |
| 1 Troy Ounce | Regular Ounces | 1.09714 oz |
| 1 Troy Ounce | Pennyweight (dwt) | 20 dwt |
| 1 Troy Ounce | Tola | 2.6667 tola |
| 1 Gram | Troy Ounces | 0.03215 ozt |
| 1 Kilogram | Troy Ounces | 32.1507 ozt |
| 100 Grams | Troy Ounces | 3.2151 ozt |
| 1 Tola | Troy Ounces | 0.375 ozt |
| 1 Regular Ounce | Troy Ounces | 0.9115 ozt |
For gold-specific conversions at any weight, use our gold price calculator.
Why the Difference Matters
The 9.7% difference between a troy ounce and a regular ounce is significant when buying or selling precious metals:
Scenario 1: Buying Gold
If gold is quoted at $4,600 per troy ounce and you mistakenly calculate value using regular ounces:
- Correct (troy oz): 31.1g × $147.88/g = $4,600
- Incorrect (regular oz): 28.35g × $147.88/g = $4,193
You'd overpay by $407 per ounce if you confused the units. This matters when verifying dealer pricing or calculating the value of gold items weighed on a household scale.
Scenario 2: Selling Scrap Gold
If you weigh your gold on a kitchen scale (which reads in regular ounces) and price it using per-troy-ounce quotes:
- 1 regular ounce of gold on your scale = 0.9115 troy ounces
- At $4,600/troy oz, the correct value is $4,600 × 0.9115 = $4,193 — not $4,600
A dealer paying you the correct amount isn't cheating you. Your scale reads lighter because a troy ounce contains more gold than a regular ounce. For accurate gold valuations, see our gold karat calculator or gold scrap calculator.
Scenario 3: Comparing Prices
If a dealer quotes silver at "$53 per ounce" and another at "$1.70 per gram":
- $53 ÷ 31.1035g = $1.704/g ✓ (these are the same price — troy ounce basis)
- $53 ÷ 28.35g = $1.870/g ✗ (wrong — this uses regular ounces)
Always divide by 31.1035 (troy ounce in grams) when converting precious metals prices to per-gram.
Other Units Used for Precious Metals
The troy ounce is the global standard, but several regional units are also common:
| Unit | Weight | Where Used | Equivalent |
|---|---|---|---|
| Troy Ounce (ozt) | 31.1035g | Global standard | 1 ozt |
| Gram (g) | 1g | Japan, China, Europe | 0.0322 ozt |
| Kilogram (kg) | 1,000g | Large bars (LBMA Good Delivery) | 32.15 ozt |
| Tola | 11.664g | India, Pakistan, Middle East | 0.375 ozt |
| Pennyweight (dwt) | 1.555g | US/UK jewelry trade | 1/20 ozt |
| Baht | 15.244g | Thailand | 0.49 ozt |
| Chi | 3.75g | Vietnam | 0.1206 ozt |
| Mesghal | 4.608g | Iran | 0.1481 ozt |
Different countries price gold in different units. In India, gold is quoted per 10 grams. In Japan, per gram. In Thailand, per baht. The troy ounce is the exchange standard that connects all of these — every local price can be derived from the spot price per troy ounce plus a currency conversion.
Common Precious Metal Weights
Here's what common gold and silver products weigh in troy ounces:
| Product | Troy Ounces | Grams |
|---|---|---|
| 1 oz Gold American Eagle | 1 ozt | 31.1g |
| 1 oz Gold Canadian Maple Leaf | 1 ozt | 31.1g |
| 10 oz gold bar | 10 ozt | 311g |
| 1 kg gold bar (LBMA Good Delivery) | 32.15 ozt | 1,000g |
| 400 oz gold bar (London Good Delivery) | 400 ozt | 12,441g (~27.4 lbs) |
| 1 oz American Silver Eagle | 1 ozt | 31.1g |
| 100 oz silver bar | 100 ozt | 3,110g (~6.9 lbs) |
For current prices of these products, see the gold price per gram and silver price per gram conversion tables.
How to Weigh Gold Accurately
If you need to weigh gold or silver at home:
- Use a jeweler's scale — These read in grams and troy ounces. Available online for $10-30.
- Convert kitchen scales — If your scale reads in regular ounces, multiply by 0.9115 to get troy ounces. If it reads in grams, divide by 31.1035.
- Account for purity — Pure gold (24K) weighs the same as 18K gold on a scale, but contains less actual gold content. Multiply weight × purity to get the gold content.
- Use a calculator — Our gold karat calculator handles weight and purity conversions automatically.
Frequently Asked Questions
How many grams is a troy ounce? One troy ounce equals exactly 31.1034768 grams. This is the international standard (ISO 31-1) used by all precious metals markets. A regular (avoirdupois) ounce is 28.3495 grams — about 10% lighter. When gold is quoted at "$4,600 per ounce," it means per troy ounce (31.1g), not per regular ounce (28.35g).
Why is a troy ounce different from a normal ounce? They come from different historical measurement systems. The troy system originated in medieval Troyes, France and was adopted specifically for precious metals and coinage. The avoirdupois system became the standard for all other goods. Both survived because precious metals markets standardized on troy before the metric system was widely adopted, and the cost of switching now outweighs any benefit.
Is a troy ounce heavier or lighter than a regular ounce? A troy ounce is heavier — 31.1g vs 28.35g (about 10% more). However, a troy pound is lighter than a regular pound because a troy pound contains only 12 troy ounces (373g) while a regular pound contains 16 regular ounces (454g). This asymmetry is a common source of confusion.
Do I need to know about troy ounces to invest in gold? If you buy gold ETFs (like GLD or IAU), you don't need to worry about troy ounces — the fund handles everything. If you buy physical gold from a dealer, you should understand that "1 ounce" means a troy ounce (31.1g), and verify weights accordingly. Our guide to buying gold covers all purchase methods.
This guide is for educational purposes only. Always verify weights and purities independently when buying or selling precious metals.