Gold uses the Troy system of weight or mass and the troy ounce is the standard unit still used today. The name is believed to come from the French city of Troyes.
1 troy ounce = 31.103477 grams BUT
1 imperial or avoirdupois ounce = 28.349523 grams
1 metric tonne = 2,204.6 pounds
1 long ton = 2,240 pounds (imperial pounds – historically used by the British)
1 short ton = 2,000 pounds (imperial pounds – historically used by the North Americans)
The grade of gold is usually expressed as g/t – grams per tonne,
or oz, dwts, gr – ounces, pennyweights, grains per ton (now largely obsolete)
The purity or fineness of gold bullion is usually expressed in parts per 1,000:
995 – a standard gold bar is 99.5% gold
9999 – a more “pure” 99.99% gold
A standard “good delivery” gold bar from an accredited refinery has a mass of approximately 400 troy ounces or around 12.5 kg.
Pure gold is 24 carat but is too soft for jewellery.
The purity of gold used in jewellery is commonly:
22 carat ~ 91.67% gold
18 carat ~ 75% gold
14 carat ~ 58.33% gold
9 carat ~ 37.5 % gold
The purity of gold for coinage is commonly:
22 carat ~ for circulation as currency
24 carat ~ 9999 for some collectors’ coins
When gold is produced, silver is also produced but this is rarely mentioned. Even seemingly “pure” gold doré will contain some silver. In the refining process silver is removed and separate gold and silver products are produced. These include “good delivery bars” and a range of smaller bars plus coins in both gold and silver.
Troy/Metric/Imperial (Avoirdupois) equivalents
|1 troy oz||=||31.103477 grams|
|1 gram||=||0.032151 troy ounces|
|1 kilogram||=||32.150746 troy ounces|
|1 tonne||=||32,150.746 troy ounces|
|24 grains||=||1 pennyweight|
|20 pennyweights||=||1 troy ounce|
|12 troy ounces||=||1 troy pound (now obsolete)|
|1 grain||=||0.064799 grams|
|1 pennyweight||=||1.555174 grams|
|1 troy ounce||=||31.103477 grams|