Anything is 'worth' what someone will pay you for it.
Carat weight is only one of four parameters used to value diamonds. The others are cut, colour and clarity.
A single twenty-carat diamond will be worth more than many diamonds that make up a total carat weight of 20 carats.
Every diamond is valued individually, depending on the four Cs used to value diamonds, as above.
The biggest carat in a cut diamond is 20 carats. The largest diamond ever found was 530 carats.
Your answer depends on the size of the diamonds, their cut, clarity and carat weight. A single diamond weighing 20 carats will be more expensive than a collection of diamonds with a total weight of 20 carats.
A one carat diamond -- 1.00 carats -- weighs .20 grams. Can you do the math?
A 20 carat diamond weighs 20 carats. If the diamond is a round brilliant cut, it measures about 17.6 mm at the girdle.
If the diamond is a round brilliant cut, this measurement at the girdle indicates that it could weigh between .20 carats (3.8 mm) and .25 carats (4.1 mm). If the diamond is of a different cut, a jeweler can remove the diamond and give you the exact carat weight.
A carat of diamond weighs .20 grammes. Can you do the math?
A red diamond is probably the rarest colour for a natural diamond. Flawless diamonds are the rarest in clarity, and large diamonds weighing in excess of 20 carats are rare.
You're asking about carats, not carrots. Carats are units of measure used to weigh precious gem stones, including ruby and diamond. One carat weighs about .20 grams.
The millimeter size of a diamond of this weight varies, depending on the cut. If the gem is round cut, its measurement at the girdle will be between 16.3 mm (15 carats) and 17.6 mm (20 carats).
If by 20 cents you mean .20 carats, you may be able to purchase such a diamond using this example as a guideline. Today, on Blue Nile, you can purchase a .23 carat diamond and pay between US$270 and US$782, depending on the colour and clarity that you want. A .23 carat diamond is the smallest diamond available for sale at Blue Nile today.
To answer your question directly, 18k is not measured in carats.Your term '18k' is typically used to describe the purity of gold. In this case, 18k indicates that 18/24ths of the metal mix is gold, 24k, therefore, being pure gold. These karats are spelled karat.For a diamond, 18 carats indicates the weight of the diamond, one carat being equal to .20 grammes. These carats are spelled carat.
A pear shapped diamond cut that measures 4.0 x 2.0 mm weighs about .20 carats. A jeweler can give you an exact weight of the diamond in question.