Carat Weight of Gems

“The weight of a precious stone is expressed in carats, an antique unit originating in the Bazaars of the Far East, where gemstones were weighed using carob seeds.”
Seeds of the carob plant were used during antiquity to weigh gemstones.

Seeds of the carob plant were used during antiquity to weigh gemstones.

All else being equal, the bigger the gem, the higher its value. In general, color and/or optical properties such as color change or play of color are more visible in larger gemstones. Traditionally, the weight of a gemstone is expressed in carats (1 carat = 0.20 grams or 200 milligrams). For gemstones weighing less than 1 carat, their weight is expressed in units that are 100 times smaller, known as points (e.g. 50 points = 0.5 carats). Originating in the bazaars of the Far East, where carob seeds were once used to weigh gems, carat weight was standardized as one-fifth of a gram in Europe in 1907.

But why did the ancients use carob seeds to weigh gems? They were selected because of their consistent size and weight. Please do not confuse ‘carats’ with ‘karats’. Karat measures gold purity and is only related to ‘carat’ from the use of carob seeds to weigh the alloys added to pure gold. In the United Kingdom, gem ‘carat’ weight and gold ‘carat’ purity are both confusingly spelled with a ‘c’. Bigger gems are always rarer than smaller ones. A 4 carat gem is always worth far more than four 1 carat gems of the same quality. However, a group of smaller gems will cost more than a single gem of the same carat weight if the cost to facet the individual gems outweighs the difference in price. Due to their comparative rarity, pairs or rows (suites) of matched gems are more highly valued than single gems of the same size and quality.