Carat

What Is Carat?

A carat is a unit that tells us how much a gemstone weighs. It is used for diamonds and other precious stones, not for their size or shine, only for weight. Jewelers around the world use carats so everyone talks about gemstone weight in the same way.

When you hear that a ring has a 1 carat diamond, it means the diamond has a certain weight. Bigger carat numbers usually mean a heavier and often more expensive stone, but many other things also affect value, such as how clear and how well cut the stone is.

Definition

In modern measurement, one carat is exactly:

• 0.2 grams or
• 200 milligrams

So:

• 5 carats equal 1 gram
• 0.5 carat equals 100 milligrams

Gem traders also use a smaller unit called a point. Points are used for finer detail in diamond weight.

• 1 carat equals 100 points
• 0.25 carat equals 25 points
• 0.75 carat equals 75 points

Remember, carat is a unit of mass or weight, not of size. Two gemstones can have the same carat weight but look different in size if they are cut in different shapes.

History / Origin

The word carat comes from the name of a tree. Long ago, people used seeds from the carob tree as tiny weights to measure precious stones.

Carob seeds were chosen because people believed the seeds were almost all the same weight. Traders would balance a gemstone on a simple scale with carob seeds on the other side. The number of seeds needed to balance the stone told them its weight.

Over time, different regions used different versions of the carat, so the value was not always the same from one country to another. This caused confusion in trading.

In the early 1900s, many countries agreed to make the carat part of the metric system. In 1907, the metric carat was fixed as exactly 200 milligrams. This clear definition helped make gemstone trading more fair and easier between countries.

Symbol & Abbreviation

The most common symbol for carat is:

• ct for one carat
• cts for several carats

Examples:

• 1 ct diamond
• 2.5 cts total weight for a bracelet

Important difference

Carat is not the same as karat even though they sound alike in English.

• Carat (ct) measures gemstone weight
• Karat (K or kt) measures how pure gold is

So a ring could have a 1 ct diamond set in 18 K gold. Here 1 ct talks about the weight of the stone, and 18 K talks about gold purity.

Current Use Around the World

Today the metric carat is used almost everywhere for weighing gemstones. It is the standard unit in the diamond and colored stone markets.

You will see carats used for:

• Diamonds in rings, earrings, necklaces, and bracelets
• Colored gemstones such as sapphires, rubies, emeralds, and many others
• Loose stones sold to jewelers or investors

Some common ways jewelers describe weight are:

• Single stone weight for one gem, for example 0.90 ct diamond
• Total carat weight (TCW or CTW) for many stones together in one piece of jewelry, for example 1.50 ctw for all diamonds in a ring

Standard carat weights help people compare stones. A buyer in one country and a seller in another country know they are talking about the same thing when they use carats.

Example Conversions

Here are some useful conversions between carats and other weight units.

Carats to grams

Use this rule:

grams = carats × 0.2

Grams to carats

Use this rule:

carats = grams × 5

Carats to milligrams

milligrams = carats × 200

• 0.10 ct equals 20 mg
• 0.25 ct equals 50 mg
• 1 ct equals 200 mg

Carats to ounces (approximate)

Some people also like to compare to ounces. One ounce is about 28.35 grams.

Steps to convert carats to ounces:

1. Convert carats to grams using grams = carats × 0.2
2. Convert grams to ounces using ounces = grams ÷ 28.35

Example for a 1 ct stone:

• 1 ct equals 0.2 g
• 0.2 g ÷ 28.35 is about 0.007 ounce

Related Units

Carat connects to several other units and ideas that are common in jewelry and metal trading.

• Gram (g) the main metric unit for weight. 1 ct equals 0.2 g.
• Milligram (mg) a very small weight unit. 1 ct equals 200 mg.
• Point a small unit used only for gemstones. 1 ct equals 100 points.
• Karat (K or kt) a unit for gold purity, not the same as carat.
• Ounce (oz) a larger unit often used in metal trading. 1 ct is much smaller than 1 oz.

When you study gemstones, you often see carats together with other quality factors, sometimes called the 4 Cs of diamonds:

• Carat weight
• Cut how well the stone is shaped
• Color how clear or colored it is
• Clarity how many tiny marks or inclusions it has

Carat is just one part of this group. A smaller stone with better cut, color, and clarity can cost more than a larger stone with poor quality.

FAQs

Is a carat a measure of size or weight?
A carat measures weight, not size. Two stones that each weigh 1 ct can look different in size if they are cut in different shapes or styles.

How many grams are there in 1 carat?
There are 0.2 grams in 1 carat. If you know the carats, you can multiply by 0.2 to get grams.

How many carats are there in 1 gram?
There are 5 carats in 1 gram. Multiply the number of grams by 5 to find the number of carats.

What is the difference between carat and karat?
Carat with a c and symbol ct measures how heavy a gemstone is. Karat with a k and symbol K or kt measures how pure gold is. They are different units for different things.

Does a higher carat always mean a better diamond?
Not always. A higher carat means a heavier stone, but quality also depends on cut, color, and clarity. A smaller but high quality diamond can look more beautiful and be more valuable than a larger low quality one.

Why do some diamonds weigh 0.99 ct instead of 1.00 ct?
Small changes in carat weight can make big price changes. Sometimes a stone is cut just under a round number like 1.00 ct to save more of the rough stone or to reach a certain price level. To the eye, 0.99 ct and 1.00 ct usually look almost the same size.

What does total carat weight mean on a jewelry label?
Total carat weight, often written as TCW or CTW, is the sum of the carat weights of all gemstones in the piece. For example, a ring with many small diamonds might say 1.00 ctw even though no single stone is 1 carat.

Can two 1 carat stones look different in size?
Yes. A deep cut stone puts more weight in the bottom part and may look smaller from the top. A shallow cut stone may look wider but can have less sparkle. Both can still weigh 1 ct.

Is the carat unit the same in every country?
Yes, in modern trade the metric carat is used almost everywhere and is always exactly 200 milligrams. This standard makes trading fair and clear across countries.

How can I quickly estimate carats from grams without a calculator?
You can remember that 1 g is 5 ct. So half a gram is about 2.5 ct, and 0.2 g is 1 ct. For a rough idea, multiply grams by 5 or divide by 0.2 in your head.