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Weights Used in Precious Metals & Jewellery

One Kilo Credit Suisse Gold Bar
One Kilo Credit Suisse Gold Bar


The carat is used to measure the weight of diamonds and other gemstones.
Since 1st April 1914 a carat has been standardised as 1/5 of a gram (.20 grams). It is sometimes called a metric carat.
A UK carat (since 1913) is 0.259 195 64 gram or 4 grains..
Because diamonds and other gemstones are expensive, it is necessary to use subdivisions of the carat. It is usually subdivided and recorded to 2 decimal places, a hundredth of a carat is known in rather unmathematical trade jargon as a "point". Half a carat is therefore written .50 carats or 0.50 carats, and would be referred to as 50 points.
In ancient times, there were various values for the carat, which ranged from 0.1885 to 0.2135 grams.

A gram or gramme is a standard metric unit of weight. There are obviously 1000 grams per kilogram.

An ancient unit which was originally based on the weight of a grain of wheat. The grain is the smallest unit of weight in the avoirdupois, troy, and apothecaries systems.
4 grains = 1 UK carat
3.086 471 670 6 grains = 1 metric carat
24 grains =1 pennyweight
480 grains = 1 troy ounce
5760 grains = 1 troy pound
437.5 grains = 1 ounce avoirdupois
7000 grains = 1 pound avoirdupois
1 grain = 0.0648 grams (0.06479891)
15.432 grains = 1 gram

Imperial System
A British system developed and refined from the earlier Roman systems used in Britain during the middle ages.
In 1824 the troy pound was defined or confirmed.
In 1863 the Imperial or avoirdupois pound was redefined as 0.45359237 kilograms.
20 stones avoirdupois = 1 ton avoirdupois
14 pounds avoirdupois = 1 stone avoirdupois
16 ounces avoirdupois = 1 pound avoirdupois
1 ounce avoirdupois = 28.349523 grams approx.
1 pound avoirdupois = 453.59237 grams
1 ton avoirdupois = 2240 pounds avoirdupois

A system historically used for measuring the weight of drugs, precious metals and gemstones. The name comes from the French city of Troyes.
480 grains = 1 ounce troy
31.1035 grams = 1 ounce troy
12 troy ounces = 1 troy pound
20 pennyweights (dwt) = 1 ounce troy
1 pound = 373.242 grams
1 pound = 5760 grains

The pennyweight was the weight of a silver penny in medieval England. When pennies were introduced in England in the 8th century, their original weight is believed to have been 24 grains. This was gradually reduced, in at least thirteen stages until it reached 7.27 grains by 1816.
According to one knowledgeable source, the pennyweight was introduced by Henry III in 1266 as the weight of 32 grains of wheat. We believe this may simply have been clarifying and codifying an existing standard.
24 grains = 1 pennyweight
20 pennyweights = 1 ounce troy
240 pennyweights = 1 pound troy
It is no coincidence that there were 240 pennies to the English pound , and 240 silver pennies were equivalent to a pound of silver, or that the word sterling applies both to the english pound and to a standard purity of silver.

Fine Ounces
Following this document's publication on the internet, we received an enquiry from L.L.F. of California:- "on the commodities market they quote metals in "fine ounces" what is that and how does it differ from say a troy ounce?"
The simple answer is that "fine ounce" is a lazy or shorthand way of saying " a troy ounce of fine..."
In this sense "fine" means pure.

One Pound = 240 Coins
According to one well researched source, in mediaeval times, a pound often meant 240 coins, so that in england a pound would be 240 pennies, whereas in Venice it was possible to have a pound (lira di grosso) of large coins (grossi) consisting of 240 grossi, and this was worth 32 times the value of a pound (lira de piccioli) consisting of 240 small coins (one piccolo). The value and weight would have been proportional to each other.

Uncia & Unciae
The word ounce comes from the Latin word uncia (plural unciae), meaning one twelfth, therefore logically speaking there should always be 12 ounces per pound in any system using both weight names. In this respect, the troy system is superior to the avoirdupois system.

Mass v. Weight
In this page, we have referred to weight and mass as being interchangeable as though they were the same. They are not, mass is a measurement of the amount of matter in an object. Weight is the force exerted by the mass of the object due to gravitational attraction.

Which is heavier

An ounce of gold (or other precious metal) or an ounce of lead (or almost anything else)? The correct answer is the gold, because it is weighed in troy ounces.
Which is heavier, a pound of gold (or other precious metal) or a pound of lead (or almost anything else)? The correct answer is the lead, because it is weighed in avoirdupois pounds.
You have 4 weights (or other article), one made of gold weighing 1 pound, one lead weighing 1 pound, 1 gold weighing 1 ounce, 1 lead weighing 1 ounce. Which of the four is the heaviest and which is the lightest? The correct answer is the lead 1 ounce weight is the lightest, and the lead 1 pound weight is the heaviest!

Is a Troy Ounce the Same as a Regular Ounce?

If you want to buy or sell gold, other precious metals, or gemstones, you will want to check the current ounce price to determine its value.  However, don’t think that you can get an accurate dollar amount by weighing your gold on a postage scale, for instance, because an ounce of gold is called a troy ounce and is very different from the avoirdupois ounce that is commonly used in the United States.

NOTE:  While most of the world uses the metric system, the United States primarily uses the U.S. customary system (also called the American system) to measure weight.


Definition of Avoirdupois Ounce

The avoirdupois ounce (commonly referred to, simply, as an ounce) is the one you use when you weigh fruits or vegetables at the grocery store or weigh yourself on your bathroom scales.  There are 16 ounces in an avoirdupois pound. 

Avoirdupois ounce is abbreviated oz.

1 avoirdupois ounce = .911458333 troy ounces, or 437.5 grains or 28.349523125 grams


Definition of Troy Ounce

Gemstones and precious metals such as gold, silver, and platinum are sold by the troy ounce.  It is heavier than the avoirdupois ounce. 

Troy ounce is usually abbreviated t oz or sometimes oz t.

1 troy ounce = 1.097142857 avoirdupois ounces, 20 pennyweights, 480 grains, or 31.1034768 grams

1 kilogram  = 32.15 troy ounces

NOTE:  There are 12 troy ounces in a troy pound, as opposed to 16 avoirdupois ounces in an avoirdupois pound.  Therefore, a troy pound is lighter than an avoirdupois pound.  However, the troy pound is no longer being used which helps a lot!


Definition of Grain

A grain is a unit of weight in both the U.S. customary system and the troy system that weighs the same under both systems. 

Its abbreviation is gr

1 unit of grain = 0.002285 ounces or 0.06479891 grams


Definition of Pennyweight

Jewelers use the pennyweight in calculating the amount and cost of precious metals used in fabricating or casting jewelry.  Dentists still use the pennyweight as the measure of precious metals in dental crowns and inlays.  It has no relation to penny coins.

Pennyweight is usually abbreviated dwt or pwt, and occasionally PW. Why is dwt the most common abbreviation? The “d” was taken from the ancient Roman penny-like coin denarius and was the abbreviation for the penny before the decimalization of the British monetary system.  Then it was used as an abbreviation for pennyweight and still is.

20 pennyweights = 1 troy ounce

1 pennyweight = 1/20 of a troy ounce, 24 grains, 7.777 carats, approximately 0.055 ounces, or 1.55517384 grams


How to Convert Avoirdupois Ounces to Troy Ounces

Multiply the number of ounces x .912 to get the approximate number of troy ounces; for example, 4.50 ounces x .912 = 4.10 troy ounces.