Carat and karat measure different things. Carat is gemstone weight: one carat equals 0.2 grams. Karat is gold purity in parts out of 24: 24K is pure gold, 18K is 75% gold and 14K is 58.5%. A 14K ring with a 1 carat diamond uses both, and the numbers are unrelated.
Carat and karat are pronounced the same and appear side by side on jewelry labels, so it is easy to assume they mean the same thing. They do not. One measures the weight of a gemstone and the other measures the purity of gold. This guide explains each term with examples, what cttw means, and how to read both on a label.
What is the difference between carat and karat?
Carat and karat sound the same but measure two different things. Carat is a unit of weight for gemstones: one carat equals 0.2 grams, or 200 milligrams. Karat is a measure of gold purity, expressed in parts out of 24: 24 karat is pure gold, 18 karat is 18 parts gold out of 24, and 14 karat is 14 parts out of 24.
So a ring described as a 14K gold ring with a 1 carat diamond uses both words in one sentence. The 14K tells you about the metal, the 1 carat tells you about the stone, and neither number says anything about the other.
0.2 g
The weight of one metric carat
100
Points in one carat; a 0.50 ct stone is 50 points
24
Parts in the karat scale; 24K is pure gold
What does carat mean for a diamond?
Carat measures how much a diamond or other gemstone weighs. The metric carat was standardized at 200 milligrams in the early twentieth century, and each carat divides into 100 points, so a 0.25 carat diamond is often called a 25-pointer. Weights are usually given to two decimal places, such as 0.70 ct or 1.02 ct.
Carat is weight, not size. Two diamonds of the same weight can look different sizes depending on their shape and how they are cut: a shallow-cut stone spreads its weight across a wider face, while a deep-cut stone hides weight below the girdle. As a rough guide, a well-cut one carat round diamond measures about 6.5 millimeters across. Different gemstones have different densities, so a one carat sapphire is slightly smaller than a one carat diamond.
Small differences in weight are hard to see. A 0.90 carat diamond and a 1.00 carat diamond of the same cut differ by only a fraction of a millimeter across the top, which is why many buyers look just below round-number weights such as half a carat or one carat. If face-up size matters most, compare millimeter measurements on the grading report rather than carat weight alone.
Carat is one of the 4Cs, alongside cut, color and clarity. A larger carat weight raises value because large diamonds are rarer, but cut quality has more effect on how much a diamond sparkles. Mined and laboratory-grown diamonds have the same density, so a one carat stone of either kind is the same size; the guide to whether a lab-grown diamond is a diamond explains how the two compare.
What does total carat weight mean?
On jewelry with more than one stone, you will often see cttw, which stands for carat total weight. It is the combined weight of every diamond in the piece. A pair of studs marked 1 cttw holds two diamonds of about half a carat each, and a cluster ring marked 1 cttw may hold dozens of small diamonds that add up to one carat.
That distinction matters, because a single one carat diamond and one carat of small diamonds look very different and are valued very differently. When comparing pieces, check whether the weight refers to a center stone or to the total. Weights stated as fractions, such as 1/2 cttw, are less precise than decimals, so a fraction can cover a small range on either side of the figure.
Before You Compare
Read the weight and the qualifier together. A 1 cttw ring, a 1 ct center stone and a 1 ct lab-grown diamond are three different descriptions, and each tells you something specific about what you are buying.
What does karat mean for gold?
Karat tells you how much of a gold alloy is pure gold. Pure gold is too soft for most jewelry, so it is mixed with metals such as silver, copper, zinc or palladium for strength and color. The karat number says how many of 24 parts are gold. 10K is 41.7% gold, 14K is 58.5%, 18K is 75% and 22K is 91.6%. Pieces are often stamped with the matching fineness number instead: 417, 585, 750 or 916.
A higher karat means more gold, a richer color and a softer metal; a lower karat means more alloy, a paler color and a harder metal. That is why 14K is so common for rings worn every day and 18K is popular for earrings and pendants. The guide to 14K vs 18K gold covers the practical differences.
| Term | Carat | Karat |
|---|---|---|
| What it measures | Weight of a gemstone | Purity of gold |
| Scale | 1 carat = 0.2 grams = 100 points | Parts of gold out of 24 |
| Abbreviation | ct, or cttw for total weight | K or kt |
| Applies to | Diamonds, sapphires and other gemstones | Gold only |
| Higher number means | A heavier stone | More gold in the metal |
| Example on a label | 1.00 cttw lab-grown diamond | 14K yellow gold |
In the United States, gold described simply as gold must be 24 karat, and lower purities must state their karat. The guide to telling whether jewelry is real gold explains how to read karat stamps.
Why are the two words so easy to confuse?
They share a history. Both words come from the Greek keration, the seed of the carob tree, which was once used as a counterweight for weighing small, precious things. Over time the same root gave jewelers a unit of weight for gems and a way of expressing gold purity as a fraction of 24.
Spelling adds to the confusion. American English uses karat for gold and carat for gemstones. British English and many other countries use carat for both, so a UK listing may describe 18 carat gold. The context makes the meaning clear: if the word describes gold, it means purity; if it describes a stone, it means weight.
Pearls add one more twist. Natural pearls were historically weighed in grains, a quarter of a carat, though most pearls today are sold by size in millimeters.
How do you read both on a jewelry label?
Take a description such as 14K white gold 1.00 cttw lab-grown diamond studs. 14K white gold tells you the metal: 58.5% gold, alloyed to a white color. 1.00 cttw tells you the combined weight of the diamonds in the pair. Lab-grown tells you the diamonds' origin, which must be disclosed when they are sold.
Reading labels this way makes comparisons easier. A higher karat changes the metal; a higher carat weight changes the stone. Neither one tells you about cut, color or clarity, which is where grading reports come in. The guide to evaluating diamond quality covers the rest of the 4Cs, and the complete diamond buying guide brings them together.
"A metric 'carat' is defined as 200 milligrams."
Gemological Institute of America, GIA 4Cs: Diamond Carat Weight
Further reading: FTC Jewelry Guides on gold karat, 16 CFR 23.3. GIA also notes that each carat divides into 100 points. The FTC Guides set the separate rule for gold: anything less than 24 karat must state its karat.
In Short
1Carat is gemstone weight: 1 carat = 0.2 grams = 100 points.
2Karat is gold purity out of 24: 14K is 58.5% gold, 18K is 75%, 24K is pure.
3Cttw is the total weight of all stones in a piece, not the size of the center stone.
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Carat weighs the stone and karat measures the gold. Read both on every label, and check whether a carat figure refers to one stone or the total. Every order ships free with a 30-day return policy.
Frequently Asked Questions
01
Is gold measured in carat or karat?
Gold purity is measured in karat in the United States, written K or kt, as in 14K or 18K. In the UK and many other countries the same measure is spelled carat, so 18 carat gold and 18 karat gold mean the same thing. Gemstones are always weighed in carat.
02
What does 1 carat mean?
One carat means a gemstone weighs 0.2 grams, or 200 milligrams. It describes weight rather than size; a well-cut one carat round diamond measures about 6.5 millimeters across, but shape and cut proportions change how large a stone of that weight looks.
03
What does cttw mean on jewelry?
Cttw on jewelry means carat total weight: the combined weight of every diamond or gemstone in the piece. A pair of 1 cttw studs holds two stones of about half a carat each, and a 1 cttw cluster ring may hold many small stones.
04
Is a higher karat better?
A higher karat means more gold, a richer color and less alloy, which suits sensitive skin. It also means a softer metal that scratches more easily. For rings worn every day, 14K is often the better balance; 18K suits earrings, pendants and special pieces.
05
Does carat measure the size of a diamond?
Carat measures a diamond's weight, not its size. Size follows weight closely for a given shape and cut, but a shallow-cut stone can look larger than a deeper one of the same carat weight. Millimeter measurements on a grading report show the actual dimensions.
06
Are lab-grown diamonds measured in carats?
Lab-grown diamonds are measured in carats exactly like mined diamonds, because they are the same material with the same density. A one carat lab-grown diamond and a one carat mined diamond weigh the same and are the same size for the same cut.