A Guide to Jewellery Weighing Units
Jewellery scales and balances are unique in the way that they can weigh using a wider range of units than a regular weighing scale. Many of these units are specific to a certain subject or material, such as gold, diamond or gemstones, and in this blog we’re going to breakdown some of the most widely used.
Before we go on, it’s important to note that many of these units are centuries old and so differ greatly between region and country. For this reason, anyone purchasing jewellery, precious metals or gemstones using a handful of these units should check what it converts to in metric or imperial measurements prior to exchange. It must also be noted that this is in no way a comprehensive guide to weighing units used in the wolrdwide jewellery industry, as there are many countries that have their own specific units of mass.
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The metric system is used in the majority of countries around the world and is a generally accepted way of measuring jewellery, precious metals and gemstones. All jewellery scales within the UK will use metric measurements although many will also feature units such as troy ounces or carats for weighing specific materials.
A carat is a unit that is predominantly used for weighing gemstones, such as diamonds, rubies, emeralds and quartz, and is equal to 0.2g (or 200mg).
For diamond measurement, the carat is the most important of the four Cs (carat, cut, colour and clarity) and greatly determines the value of the stone. However, since there are more factors at play during diamond measurement, two diamonds with the same carat weight can differ drastically in value.
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Commonly mistook as a carat, a karat is its own separate weighing unit that is used to measure the purity of gold and other precious metals. Soft metals such as gold are often mixed with harder metals like silver or copper to craft and shape jewellery. The ratio of the gold to the other metal is measured in parts, where the highest possible level of purity is 24 karats. For example, an 18 karat ring is 18 parts gold and 6 parts something else.
Troy Ounces (t oz)
The troy ounce is a weighing unit used to measure the weigh of precious metals such as gold, platinum and silver. This is not to be mistaken for a regular ounce that would be used to measure everyday subjects like sugar or flour, as a troy ounce is equal to 31.1 grams and a regular ounce is equal to 28.349 grams. Whilst this difference may not seem like much, for larger or more expensive items it’s crucial to understand the difference between the two.
Pennyweights are a generally less popular unit of measurement that belongs to the troy measurement system - along with the troy ounce – where one pennyweight is the equivalent to 1/20 of a troy ounce (roughly 1.5 grams). Like the troy ounce, pennyweights are used to weigh precious metals, with the original English penny being equivalent to 1 pennyweight of pure silver (hence the name). Nowadays, pennyweights are reduced to more specialist metal traders, with many choosing to use grams or troy ounces instead.
A centuries old unit originating from Japan, the momme is now widely used for measuring silk and pearls. Often, pearls are divided into groups based on quality and size, and the individual group is given a price per momme. One momme is the equivalent to 3.75 grams, whilst 1000 momme is equal to another centuries old Japanese unit; the kan.
Taking its name from a ‘grain’ of wheat or barley, the grain is a unit that originated centuries ago where cereal grains were actual legal definitions of mass. In present day, it is equal to exactly 64.79891 milligrams and is almost obsolete, although can be used to weigh out much smaller amounts of precious metals such as gold foil.
The tael is a unit of measurement that originated from China, although has been used in other countries with a different value. In Hong Kong and Singapore, the tael is equivalent to 37.7994 grams and is still used to weigh out silver and gold.
Tola is a Hindi term which is used in India, Nepal, Pakistan, Bangladesh and Singapore to measure out gold and silver, most commonly gold bars. In present day it is equal to 11.7 grams, although there may be slight variations of this depending on what country you are in. Many Indian jewellers have rounded it down to 10 grams to make it easier to convert using the metric system. For this reason, its recommended to ask your jeweller how many grams are in 1 tola before you buy.
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