Everything You Ever Wanted to Know About Precious Metals Measurements but Didn't Know Who to Ask
"Troy" ounces explained
Ever hear the old riddle, "Which weighs more -a pound of gold or a pound of feathers?" You're supposed to answer that they weigh the same, but this isn't necessarily the case. Read on:
The "Troy" ounce (oz t) is an imperial unit of measure, now generally only used for weighing precious metals. It originated in the Roman empire in a system used for measuring their bronze currency. A single unit was a pound, and there were 12 'unicas' (or ounces) to a pound. Later standardization would change the common measurement system to be based on 16, which is where we get the "avoirdupois" ounce. This is now commonly used to measure everything BUT precious metals.
A single troy ounce is exactly 31.1034768 grams, and an avoirdupois ounce is exactly 28.349523125 grams making the troy ounce heavier than the avoirdupois ounce by 9.7 percent. However, one troy pound (12 oz t) is actually lighter than an avoirdupois pound (16 oz) because the difference in the number of avoirdupois ounces to the pound is more than enough to overcome the shortcoming of its ounce weight to the Troy ounce.
It is important to mention that while many precious metals bars and rounds do not mention the word 'troy' in their design, it is common knowledge in the industry that this unit is used, so it is sometimes omitted. However, since copper is not a precious metal, it is normally measured in avoirdupois ounces and pounds.
So next time you hear that riddle, you can answer that a pound of feathers (avoirdupois pound) indeed does weigh more than a pound of gold (troy pound)!
Just remember: ALL PRECIOUS METALS TRANSACTIONS ARE CALCULATED IN TROY OUNCES!
The Pennyweight (abbrev. dwt) is another unit of measurement used for precious metals, but is more commonly used in scrap gold purchases and in measuring the amount of metal in jewelry and dental fillings. It is usually not used in measuring precious metals bullion and coins. A pennyweight is equal to 24 grains, or 1/20 of a Troy ounce…so 20 pennyweight is equal to one troy ounce.
|A convenient weight chart|
|1 ounce troy||31.1034768 grams|
|1 ounce troy||20 dwt (pennyweight)|
|12 ounces troy||1 pound troy|
|32.1507 ounces troy||1 kilogram|
|1 ounce avoirdupois||28.349523125 grams|
|1 ounce avoirdupois||18.2291 dwt (pennyweight)|
|1 ounce avoirdupois||0.9114 ounces troy|
|16 ounces avoirdupois||1 pound avoirdupois|
|35.27396 ounces avoirdupois||1 kilogram|
Carat Weight and Karats in Gold
It is first important to note that diamonds are weighted in 'carats' (also confusingly spelled 'karats'), and that carat weight is different from the karats we are talking about here. One 'carat' is 0.2 grams, so a 3 carat diamond weighs 0.6 grams.
A karat (K) in gold is a measurement of the purity of gold in an alloy, namely the percentage of pure gold as a whole number with a base of 24. The purest of pure gold is 24K, while jewelry is often much less pure (and much stronger). Jewelry often comes in 10K, 14K, and 18K fineness.
Vintage coin gold is generally at or above 90% pure and below 95% pure because gold is a very soft metal and damages easily. Other metals, such as silver and copper are added to gold to harden it for circulation. A good example of 90% pure coin gold is our United States Liberty gold coins, Indian gold coins, and Saint-Gaudens double eagles minted prior to 1933.
Bullion gold is usually 24K, or 99.9% fine (with a primary exception of Gold and Platinum Eagles – explanation below), allowing 0.01% for trace impurities. Refineries have found methods of extending this purity to 99.999% fine through special chemical and electrolysis processes, however 99.9% is the standard fineness of "pure" gold.
American Gold and Platinum Eagles are an exception to the 99.9% fineness in that they are less pure (to make the coins more durable) but the overall weight of the coins are increased so that the total amount of pure metal in the coins matches the even weight amount (again in troy ounces) minted into the coin's design. For instance, a one-ounce Gold Eagle is minted in an alloy consisting of 91.67% pure gold (22K gold) with the remainder of its composition in silver and copper, but it still contains one full troy ounce of 99.9% pure gold. The overall weight of the coin (to compensate for the other metals) is 1.0909 troy ounces.
What is AGW?
AGW is an abbreviation for "actual gold weight." It takes into account that coin gold is not pure, and coins are often minted in weights that are equally divisible units of troy ounces. The problem here is that there is not a troy half ounce of pure gold in a .900 fine gold coin weighing 1/2 troy ounce. In this instance, there is only .450AGW in this coin – 0.45 oz t of 24K gold. Displaying AGW of gold coins helps standardize the exact amount of pure gold in coins of different weights and fineness.
Actual weight is also used for silver and platinum coins and is abbreviated (ASW) and (APW) respectively.
|Karat to Fineness Chart|
|8K||.333 or 33.3% pure|
|10K||.416 or 41.6% pure|
|14K||.586 or 58.6% pure|
|16K||.666 or 66.6% pure|
|18K||.75 or 75% pure|
|22K||.916 or 91.6% pure|
|24K||.999 or 100% pure|
|Pureness of common worldwide gold coin types|
|U.S. Gold (pre-1933)||0.9||21.6K||various|
|Mexican 20 Peso||0.9||21.6K||0.482|
|Russian 10 Roubles||0.9||21.6K||0.249|
|Austrian 100 Corona||0.9||21.6K||0.98|
|Austrian 4 Ducat||0.986||23.6K||0.443|
|Swiss 20 Franc||0.9||21.6K||0.187|
|Hungary 100 Corona||0.9||21.6K||0.98|
|French 20 Franc||0.9||21.6K||0.187|
|South African 1 Rand||0.9167||22K||0.118|
|German 20 Mark||0.9||21.6K||0.23|