Carat To Kilogram Converter

1. Keep the direction on Carats to kilograms, or pick kilograms to carats or grams to carats.
2. Type the carat weight from the label, certificate or scale, such as 0.47 ct.
3. Read the kilograms at the top. Grams, milligrams, points and scientific notation appear below it.

Here is what each output means:

A carat to kilogram conversion expresses a gemstone mass given in metric carats (ct) as kilograms (kg), the SI base unit of mass. The metric carat is defined as exactly 200 milligrams, so it is a tiny fraction of a kilogram.

NIST Handbook 44 lists the carat as 200 milligrams exactly and the point as 0.01 carat, or 2 milligrams. The United States adopted this international metric carat on July 1, 1913, as NIST Circular 43 records. Before that, the carat used in the US was nearer 205.3 milligrams, and the value varied from country to country.

NIST also notes that the carat began with the carob seed. It was later standardized at 0.2 gram, or 200 mg. Today it is used for diamonds and other gemstones. This page helps jewelers, students, gem buyers and anyone filling in a form that asks for grams or kilograms.

You multiply carats by 0.0002, because each carat is 0.2 gram and a gram is 0.001 kilogram.

1. Start from the definition: 1 ct = 200 mg.
2. Change milligrams to kilograms: 200 mg = 0.2 g = 0.0002 kg.
3. Multiply the carats by 0.0002. For 2.5 ct: 2.5 x 0.0002 = 0.0005 kg, which is 0.5 g.

All of these factors are exact decimals, so the converter adds no error. Only the reading on the scale carries uncertainty.

A one carat diamond. 1 ct x 0.0002 = 0.0002 kg. That is 0.2 g, or 200 mg, and 100 points.

A three quarter carat stone. 0.75 ct x 0.0002 = 0.00015 kg, which is 150 mg or 75 points.

A parcel of rough stones. A dealer lists 250 ct. 250 x 0.0002 = 0.05 kg, or 50 g. A customs form in grams would show 50 g.

Grams back to carats. A lab balance reads 3 g. 3 x 5 = 15 ct. For other gram conversions, the kg to grams converter handles the metric steps.

Each row uses 1 ct = 200 mg exactly. Points are carats x 100, so a one third carat stone sold as 0.33 ct is 33 points.

Note that 1 ct is 20 centigrams, which the centigram to kilogram converter can confirm.

The 200 mg factor is fixed. The answer can still differ because of how the carat weight was measured and stated.

Rounding on Labels

The FTC Jewelry Guides say a diamond weight given to two decimals, such as .47 carat, should be accurate to the last decimal. A weight given as .5 carat could be anything from .495 to .504 carat.

Fractions vs Decimals

A label that says 1/2 ct is not exact. The FTC asks sellers to disclose that fractional weights are not exact and to give the range or tolerance used.

Size Is Not Mass

Carat weight is mass, not size. A 1 ct diamond fills about 56.8 cubic mm at a specific gravity of 3.52. A stone with a different density will be larger or smaller at the same carat weight.

Old Carats in Old Records

US records from before July 1913 may use the old carat of about 205.3 mg. That old carat is 2.65 percent heavier than the metric carat.

A carat measures the mass of a gemstone. A karat measures the purity of gold. The two words sound alike but have nothing to do with each other.

The FTC Jewelry Guides treat 24 karat as fine gold and require the karat fineness to be stated for gold alloys. By the same 24ths, 14 K is 58.3 percent gold and 10 K is 41.7 percent. None of these numbers can be converted to kilograms.

Reading a Gem Report

Grading reports give carat weight, while shipping and insurance forms may ask for grams. A 2.5 ct stone is 0.5 g.

Customs and Freight

Parcels of loose stones often travel with total weights in grams or kilograms. Converting 1,000 ct gives 0.2 kg.

Lab and School Work

SI units are needed for density and physics problems. A 0.5 ct sample is 1 x 10^-4 kg, ready for a formula.

Comparing Gems with Gold

Gold is sold by troy ounce or gram, not by carat. The grams to ounces converter helps turn the gram figure into ounces.

Most carat shortcuts are exact because the carat is a clean metric unit.

• Divide by 5 for grams. 15 ct / 5 = 3 g. Exact.
• Times 200 for milligrams. 0.3 ct x 200 = 60 mg. Exact.
• Divide by 5,000 for kilograms. 2,500 ct / 5,000 = 0.5 kg. Exact.
• Points to carats. Move the decimal two places: 35 points = 0.35 ct. Exact.
• About 142 carats per ounce. One avoirdupois ounce is 141.75 ct, so 142 is 0.18 percent high.

1. Treating Karat as a Weight

An 18 K ring says nothing about how heavy it is. Only a carat (ct) value converts to kilograms.

2. Reading Points as Carats

A "25 pointer" is 0.25 ct, not 25 ct. Twenty five carats would be 5 g, a hundred times more.

3. Dropping Zeros in Kilograms

1 ct is 0.0002 kg, not 0.002 kg. The scientific notation line, 2 x 10^-4 kg, helps you check.

4. Guessing Size from Carats

Two stones of the same carat weight can differ in size if their densities differ. Measure millimetres for size.

5. Using a 205 Mg Carat

Old US records may use a carat near 205.3 mg. Applying the metric factor to them understates the mass by about 2.6 percent.

The conversion is exact, because the metric carat is defined as 200 mg with no rounding.

One kilogram is exactly 5,000 metric carats. Each carat is 0.0002 kg, and 1 / 0.0002 = 5,000.

A 1 carat diamond weighs 0.2 g, or 200 mg. Five carats make one gram.

No. A carat is 200 mg of gemstone mass. A karat is a measure of gold purity, where 24 K is fine gold.

One carat has 100 points. A point is 0.01 ct, which is 2 mg.

Half a carat is 0.0001 kg, or 1 x 10^-4 kg. That is 100 mg.

The 200 mg metric carat was agreed internationally to end confusion between national carats. The United States adopted it on July 1, 1913.

For the same gem type, yes. Across different gem types, no, because denser stones pack more carats into the same size.

One avoirdupois ounce is 141.75 ct. One troy ounce, used for gold, is 155.52 ct.

It is the combined carat weight of all stones in a piece. Divide it by the number of stones only when they are the same size.

Only with a scale that reads to 0.01 g or finer, since 0.01 g is 0.05 ct. For value or grading, use a certified scale and a professional.

No. The conversion runs in your browser and nothing is sent to our servers. A result you choose to Save stays in this browser only.

• Carat = 200 milligrams exactly; point = 0.01 carat (NIST Handbook 44, 2026, Appendix C).
• Carat, metric to kilogram and gram conversion factors (NIST SP 811, Appendix B.8).
• The metric carat adopted in the United States on July 1, 1913 (NIST Circular 43, The Metric Carat, 1913).
• Carat origin in the carob seed and precious metal units (NIST Office of Weights and Measures).
• Diamond weight in carats and points, karat fineness of gold (FTC Guides for the Jewelry Industry, 16 CFR Part 23, eCFR).