How this calculator works
A carat is a metric unit of mass defined as 0.2 grams, so five carats weigh one gram. Jewellers divide a carat into 100 points, which makes 0.25 carats the same as 25 points and 0.75 carats the same as 75 points. A carat is not the same as a karat, which measures the purity of gold. The page converts between carats, points, grams and avoirdupois ounces, and multiplies the carat weight by a price per carat to give a total price. The price is arithmetic on the rate you enter; real diamond pricing is not linear, because larger and higher-quality stones command a higher price per carat. To estimate a stone weight from its measurements rather than convert a known weight, use the diamond weight calculator.
Formula
carats = weight when the weight is entered in carats. carats = grams / 0.2. carats = points / 100. carats = ounces x 28.349523125 / 0.2. points = carats x 100. total price = carats x price per carat.
Worked example
A 1.5 carat stone weighs 1.5 x 0.2 = 0.3 grams, or 150 points. At 4,000 dollars per carat it would be priced at 1.5 x 4,000 = 6,000 dollars. A half carat stone is 50 points and 0.1 grams. One avoirdupois ounce is 28.349523125 grams, which is 141.7476 carats, so a 1 ounce weight entered in the ounce mode converts to about 141.75 carats.
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Frequently asked questions
Is a carat a measure of size?
No. A carat measures mass. A one carat diamond is usually about 6.5 millimetres across when cut as a round brilliant, but the diameter depends on the cut and its depth. A shallow stone of one carat can look larger than a deep one of the same weight.
What is the difference between a carat and a point?
A point is one hundredth of a carat. A 25 point stone is 0.25 carats and a 75 point stone is 0.75 carats. The point scale is convenient for small stones and for describing half and quarter carat weights without decimals.
How many grams are in a carat?
Exactly 0.2 grams, or 200 milligrams. The metric carat was adopted in 1907 to replace the slightly different local carats that jewellers had used in different countries.
Should I use troy ounces or regular ounces?
This page uses the avoirdupois ounce of 28.349523125 grams, the ordinary ounce used for body weight and food. A troy ounce is heavier at 31.1034768 grams and is used for precious metals, not for diamonds. Choose the unit that matches your scale.