What Is a Troy Ounce?
A troy ounce is the standard unit for weighing precious metals, equal to exactly 31.1034768 grams, usually rounded to 31.1035. It is about 10% heavier than the everyday avoirdupois ounce of roughly 28.35 grams. When you see a gold, silver, platinum or palladium price "per ounce," it always means per troy ounce of pure metal.
Troy Ounce vs Standard Ounce
The ounce used in U.S. grocery stores and postal scales is the avoirdupois ounce. The two units share a name but not a weight:
| Unit | Grams | Notes |
|---|---|---|
| Troy ounce | 31.1035 | Used for precious metals worldwide |
| Avoirdupois ounce | 28.3495 | Used for most everyday goods in the U.S. |
One troy ounce equals about 1.097 avoirdupois ounces. If you weighed a one-ounce gold coin on a kitchen scale set to ordinary ounces, it would read a little over one ounce, and if the coin is 22-karat alloy, even more, because the alloy metals add weight.
The Troy Pound Is Lighter, Not Heavier
Here is a detail that surprises people: although a troy ounce is heavier than a standard ounce, a troy pound is lighter than a standard pound. That's because a troy pound contains only 12 troy ounces, while an avoirdupois pound contains 16 ordinary ounces.
- Troy pound: 12 troy ounces, about 373.24 grams
- Avoirdupois pound: 16 ounces, about 453.59 grams
In practice, the troy pound is almost never used in today's metals market. Prices and product sizes are given in troy ounces, grams or kilograms.
Other Units You'll Encounter
- Grain: the base unit of both systems, about 64.8 milligrams. A troy ounce contains 480 grains.
- Pennyweight (dwt): one-twentieth of a troy ounce, about 1.555 grams. Jewelers and scrap buyers still use it.
- Gram: common for small bars, from 1 gram up to 100 grams. To convert, divide grams by 31.1035; a 50-gram bar holds about 1.61 troy ounces.
- Kilogram: about 32.15 troy ounces. Kilo bars are common in wholesale and some retail markets.
- Tola: a traditional South Asian unit of about 11.66 grams, used for some bars sold in India and the Middle East.
Where the Name Comes From
The troy system is generally traced to medieval Europe. The most common explanation links the name to Troyes, a city in the Champagne region of France that hosted major trade fairs where merchants from across Europe met and needed consistent weights. England adopted troy weight for precious metals and coinage centuries ago, and it remained in use after the British imperial system was reformed in the 19th century. The United States also adopted the troy pound as the standard for minting coins, which is part of why the unit persists in American bullion markets today.
Today the troy ounce is defined in terms of the metric system. Since the international yard and pound agreement of 1959, the grain has been defined as exactly 64.79891 milligrams, which fixes the troy ounce at exactly 31.1034768 grams.
Why the Unit Matters When You Buy
Comparing prices
The gold spot price is quoted per troy ounce. To check a quote, divide the total price by the troy ounces of pure metal you're receiving. For gram bars, convert grams to troy ounces by dividing by 31.1035.
Fine weight vs gross weight
A product's fine weight is the amount of pure metal it contains; gross weight is the total including any alloy. A one-ounce American Gold Eagle contains one troy ounce of gold but weighs about 33.93 grams because it is 22-karat. A one-ounce Gold Buffalo, at .9999 fine, weighs very close to 31.10 grams. Our guide to gold purity and karats explains how fineness affects weight, and the gold coin sizes guide lists standard weights.
Spotting fakes
Because genuine bullion products are made to precise weights, a coin that is noticeably off is a warning sign. Our page on how to spot fake gold and silver covers weight checks along with other tests.
Metals held in retirement accounts
Federal tax law sets IRA eligibility by fineness rather than weight, but statements from custodians and depositories report holdings in troy ounces. Our page on reading a precious metals IRA statement shows how those figures are presented.
If you are working with a precious metals company such as Goldco, product listings and invoices typically state each item's metal content in troy ounces, which makes comparisons straightforward. Our overview of gold coins available through Goldco describes the products it lists.
Frequently Asked Questions
How many grams are in a troy ounce?
Exactly 31.1034768 grams, commonly rounded to 31.1035 or 31.1.
How many troy ounces are in a kilogram?
About 32.15 troy ounces.
Is a troy ounce heavier than a regular ounce?
Yes, by roughly 10%. A troy ounce is about 31.1 grams; a regular ounce is about 28.35 grams.
Why don't metals markets just use grams?
Many products are made in grams and kilograms, but the troy ounce remains the convention for global price quotes, futures contracts and most popular coins, so both coexist.