‘Carat’ is a term used to describe the weight of a diamond, and the word originates from Ceratonia siliqua, commonly known as the Carob tree.
The modern carat weighing system all started with the carob seed. It turns out that the seeds of the carob tree, which are covered like a large flat pea, are very symmetrical and the difference in weight between one and the other is negligible. Before scales and units of mass were invented, early diamond traders used the small, uniform seeds as counterweights in their balance scales. Each Carob seed had a uniform weight, equal to 0.20 grams or 200 milligrams. Their consistent weight made them a reliable source of measurement in the assessment of diamonds.
Carat weight serves as a crucial metric measure, defining the weight of a diamond. 1 carat is equivalent to 0.20 grams.
It’s important not to confuse diamond carat weight with the physical size of the diamond. Both are separate units of measurement but equally as important.
The diamond carat weight system was legally established with the introduction of the Weights and Measures Act of 1963. The Carat weight can be expressed in many different terms, but ultimately all mean the same. One Carat diamond weighs 200 milligrams, 0.20 grams, or 1/5 metric gram. Alternative expressions include:
- Decimal Weight: A quarter carat diamond is denoted as 0.25cts. Half a carat diamond is denoted as 0.50cts and a carat diamond 1.00cts.
- Fractional Carat Weight: Expressed in fractions, with 1/4 carat representing 0.25cts or a quarter of a carat. 1/2 carat, 0.50cts or half a carat.
- Points: Used for weights below a full carat, one carat divided into 100 points. For example, half a carat is expressed as 50 points.
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