Units for Weighting Gemstones

Carat:

This weight is used in the gems trade since ancient times. The name is derived from the seed (kuara) of the African Coral tree or from the kernel (Greek-kertion) of the Carob bean. Since 1907, Europe as well as America, have adopted the metric carat of 200 mg. or 0.2g. Therefore weights given for famous old diamonds often vary because local carats and not metric carats were used. The carat is subdivided into fraction (1/10 ct) or decimals (1.25ct) up to two decimal places. Small diamonds are weighed in "points" = 1/100 cts. (=0.01 cts.). The table below illustrates diametre and corresponding carat weight for diamonds cut in the modern brilliant cut. Gems with different specific gravities and different cuts obviously have different diametres.

The carat weight of gems is not to be confused with the karat used by goldsmith. In the case of gold, the karat is not a weight measure, but indicates purity. The higher the karatage, the higher the content of gold in the piece of Jewellery. The weight can be variable.

Gram:

Weight used in gems trade for lesser gemstones are for rough gem stones (for instance, quartz)

Grain:

(Latin - granum) Weight measure for pearls. Corresponds to 0.05 grams = 0.25 or 1/4 carat. Increasingly superceded by carat weights, the old Japanese weight- the Momme (=3.75 grams = 18.75 carats) is hardly used any more in Europe.

WEIGHT CONVERSION TABLE

Unit

Grams

Carats

Oz. Troy

Dwt.

Oz. Av.

Grain

1 Carat

.20

.00705478

3.08647

1 Gram

.03215

.6430

.3527

15.4324

1 Penny Weight

1.5517

0.5

.548571

1 Grain

.6479

.3240

.0020833

.041667

.0022857

1Ounce Avoirdupois

28.3495

141.75

.9114883

18.2297

437.5

Troy

373.241

1,866.12

240

13.1657

5.760

1 Pound Avoirdupois

453.295

2,267.96

145833

291.667

7.000

STANDARD ABBREVIATIONS

Avoirdupois

Av.

Milligram

Mg.

Carat

C. or Ct.

Millimetre

Mm.

Grain

Penny Weight

Dwt.

Gram

Pound

Ib.

Kilogram

Kg.

Troy