What Is Carat?
A carat is a unit used to measure how much a gemstone weighs. Jewelers use carats to tell the weight of diamonds, rubies, sapphires, emeralds, and other precious stones. One metric carat is a small amount of mass, but it is very important in the jewelry world because it affects price and value.
Definition
The metric carat is a unit of mass.
- 1 carat = 0.2 grams
- 1 carat = 200 milligrams
Gemstone weights are usually written in decimal carats. For example, a diamond might weigh 0.25 carat, 0.50 carat, 1.00 carat, or 1.25 carats. Very small stones are often called “points.”
- 1 carat = 100 points
- So 0.25 carat = 25 points
- 0.50 carat = 50 points
The carat only tells you weight, not quality. A 1 carat diamond can look good or bad depending on clarity, color, and cut.
History / Origin
The word carat comes from the name of the carob tree. Long ago, traders used carob seeds to weigh small, valuable items. They believed carob seeds had a fairly even weight, so they used them as a simple weighing tool for gold and gems.
Over time, different regions used slightly different carat values, so trade weights were not always the same. To fix this, countries agreed to standardize the carat.
- In the early 1900s many countries agreed that 1 carat would be exactly 0.2 grams.
- This metric carat was officially adopted in 1907 by the General Conference on Weights and Measures.
Today, this metric carat is used almost everywhere in professional gemstone trading.
Symbol & Abbreviation
The carat has a few common symbols and short forms.
- Main symbol in jewelry: ct
- Plural: cts or still ct in some catalogs
- Sometimes just the word “carat” is written out
Examples.
- 0.75 ct means zero point seven five carat
- 2.0 ct means two carats
Important. Do not confuse carat (ct) with karat (K or kt).
- Carat measures gemstone weight.
- Karat measures gold purity, for example 24K or 18K.
Current Use Around the World
The metric carat is now the standard unit for gemstone weight worldwide.
It is used to weigh.
- Diamonds
- Colored gemstones, such as rubies, sapphires, emeralds, opals
- Pearls
- Some types of small decorative stones
In all major jewelry markets, including the United States, Europe, Asia, the Middle East, and Africa, carats are used for both wholesale trading and retail sales. Jewelers use special digital scales that can measure weight to at least one hundredth of a carat or even finer.
While many people think of carat as a size measure, professionals remember that it is only weight. Two stones with the same carat weight can look different in size if they have different shapes or densities.
Example Conversions
Here are some helpful carat conversions and examples using simple numbers.
Carats to grams
- 1 ct = 0.2 g
- 0.5 ct = 0.1 g
- 2 ct = 0.4 g
- 5 ct = 1.0 g
- 10 ct = 2.0 g
Carats to milligrams
- 1 ct = 200 mg
- 0.25 ct = 50 mg
- 0.75 ct = 150 mg
- 3 ct = 600 mg
Carats to ounces (avoirdupois)
1 ounce is about 28.35 grams.
- 1 ct = 0.2 g ≈ 0.007055 oz
- 10 ct = 2 g ≈ 0.0706 oz
- 50 ct = 10 g ≈ 0.353 oz
Simple real life style examples
- A small diamond in a ring might be 0.10 ct, or 10 points.
- A common engagement ring center stone might be around 0.50 ct to 1.00 ct.
- Large showpiece gemstones can be 5 ct, 10 ct, or much more.
Related Units
Units related to the carat help compare and convert gemstone weights.
- Gram (g) the main metric unit of mass. 1 ct = 0.2 g.
- Milligram (mg) small metric unit of mass. 1 ct = 200 mg.
- Point used in the diamond trade. 1 point = 0.01 ct.
- Ounce (oz) used in some countries for general weight. Not common for gemstones, but useful for comparison.
- Karat (K or kt) a different unit used for gold purity, not for weight.
FAQs
What is a carat in simple words
A carat is a unit to tell how much a gemstone weighs. It is a small amount equal to 0.2 grams. Jewelers use it to describe diamond and gem weight.
Does a higher carat always mean a better diamond
No. A higher carat only means more weight. Diamond quality also depends on color, clarity, and cut. A smaller but very clear and well cut stone can look better than a bigger one with many flaws.
What is the difference between carat and karat
Carat measures gemstone weight. Karat measures how pure gold is. For example, 24K gold is pure gold, and 18K gold is a mix of gold and other metals. They are different units used for different things.
How many carats are in a gram
There are 5 carats in 1 gram. This comes from the rule that 1 carat is 0.2 grams. So 1 g divided by 0.2 g per carat equals 5 carats.
Can two 1 carat stones look different in size
Yes. Two 1 carat stones can look bigger or smaller depending on their shape, how they are cut, and the type of gemstone. Some gems are denser than others, so they can be heavier even if they look smaller.
Why do jewelers use carats instead of grams
Carats are a long used standard in the jewelry trade. They give a simple, shared way for buyers and sellers around the world to compare gemstone weights quickly without always thinking in grams.
Are pearls also measured in carats
Many pearls are measured by weight in carats, but some pearl markets also sell them by size in millimeters or by strand. It depends on local customs and the type of pearl.
Is carat weight the same as ring size
No. Carat weight is about how much the stone weighs. Ring size is about how big the ring is on your finger. They are two completely different measurements.
How accurate are carat measurements
Modern jewelry scales are very accurate. Professional grading labs and jewelers often measure to at least two decimal places, such as 0.73 ct, so weight can be known very precisely.
Can carat be used for anything other than gemstones
In modern practice, carats are mainly used for gemstones and pearls. For most other materials and everyday objects, people use grams, kilograms, or ounces instead.