Karat vs Carat: Two Different Words
Karat measures how pure gold is. Carat measures how much a gemstone weighs. A 14-karat gold ring is 14 parts gold out of 24, which is about 58.3 percent gold. A one-carat diamond weighs 200 milligrams, or one-fifth of a gram. The two words sound the same and come from the same root, so they are easy to confuse, and one piece of jewelry often has both: a 14K gold ring set with a 1-carat diamond. In the United States the spellings are kept apart. Outside the United States, "carat" is commonly used for both.
This guide explains each unit, gives the percentages and stamps for the common gold grades, shows how gemstone weight is measured down to the "point," and covers the spelling differences that trip up online shoppers.
The short version
| Karat (K) | Carat (ct) | |
|---|---|---|
| What it measures | Purity of gold in an alloy | Weight of a gemstone or pearl |
| Scale | Parts per 24 | 1 carat = 200 milligrams |
| Typical numbers | 10K, 14K, 18K, 24K | 0.25 ct, 0.5 ct, 1 ct, 2 ct |
| Higher means | More gold, softer metal | Heavier stone |
| Appears on | Gold jewelry stamps | Diamond and gemstone listings |
Karat has nothing to do with weight, and carat has nothing to do with purity. Mixing them up leads to real mistakes, such as assuming an "18 carat" ring contains a large diamond, or that a "2 karat" diamond weighs twice as much as a 1-carat one. Neither phrase means that.
What karat measures
Gold in its pure form is very soft, so jewelry is almost always made from an alloy, which is gold mixed with other metals such as silver, copper or zinc to add strength. Karat describes how many of 24 equal parts are gold.
- 24 karat is 24 parts gold, essentially pure.
- 18 karat is 18 parts gold and 6 parts other metals.
- 14 karat is 14 parts gold and 10 parts other metals.
- 10 karat is 10 parts gold and 14 parts other metals.
Because each karat is one twenty-fourth, each step is about 4.17 percent gold. The common grades work out like this:
| Karat | Parts gold | Percent gold | Common stamp |
|---|---|---|---|
| 24K | 24 of 24 | 99.9 percent | 999 |
| 18K | 18 of 24 | 75 percent | 750 |
| 14K | 14 of 24 | 58.3 percent | 585 |
| 10K | 10 of 24 | 41.7 percent | 417 |
A few notes on those numbers:
- 24K is described as 99.9 percent because even refined "pure" gold is rarely 100 percent. It is often stamped 999 for 999 parts per thousand.
- 14K works out to 58.33 percent exactly, and the common European-style stamp 585 is a rounded figure. You will see both "14K" and "585" on the same type of piece, and they mean the same thing.
- 10K works out to 41.67 percent, stamped 417.
- Other grades exist. 22K is 22 of 24 parts, about 91.7 percent. 9K, which you will see on pieces from some other countries, is 9 of 24 parts, or 37.5 percent. It is rare on American listings, where 10K is the usual lowest grade.
You can work out the gold in any piece with simple arithmetic. A 10 gram bracelet in 14K gold contains about 5.83 grams of gold, because 10 times 14 over 24 is 5.83. The rest of the weight is the alloying metals.
Reading a gold stamp
A karat or fineness stamp is how the maker states the purity. You may see:
- A number with K or kt, such as 14K or 18kt.
- A three-digit number such as 585 or 750, which is the same claim expressed in parts per thousand.
- Letters such as GF, GP, GEP, RGP or HGE, which are plating and filled marks and not solid gold marks.
The Federal Trade Commission's Jewelry Guides, at 16 CFR 23.3, allow a small tolerance when gold is tested. Articles that contain no solder have a permissible tolerance of three parts per thousand, and if the part tested contains solder the permissible tolerance is seven parts per thousand. In other words, an honest 14K piece may test a little under the exact figure, but not by much.
Plated and filled pieces follow different rules. A gold filled item must have gold making up at least 1/20th of the weight of the metal in the entire article, with the karat marked, and a stamp like 14K GF describes a layered piece. Our guide to gold filled vs gold plated explains the difference, and our guide to how to tell if gold is real shows how to check marks and test a piece.
What carat measures
A carat is a unit of mass used for gemstones and pearls. It equals exactly 200 milligrams, or 0.2 grams. Five carats weigh one gram.
The carat is divided into 100 points. One point is therefore one hundredth of a carat, or 2 milligrams. That is why a listing may say a diamond weighs 0.75 carat, "75 points" or "three-quarters of a carat," which are all the same statement.
| Weight | Points | Milligrams |
|---|---|---|
| 0.25 ct | 25 points | 50 mg |
| 0.50 ct | 50 points | 100 mg |
| 0.75 ct | 75 points | 150 mg |
| 1.00 ct | 100 points | 200 mg |
| 2.00 ct | 200 points | 400 mg |
Carat weight measures mass, not size. A stone's visible diameter depends on how it is cut, so two stones with the same carat weight can look different, and a well-proportioned stone can look larger than a deeper cut of the same weight. For a diamond, weight is only one of the four Cs. Color, clarity and cut matter as well, and our guides to the diamond color chart from D to Z and to what each diamond clarity grade means cover two of the others.
Total weight, or "carat total weight"
Jewelry with several stones is often listed by total carat weight, sometimes written CTW or TCW. A ring described as "1 carat total weight" with a cluster of small diamonds does not contain one 1-carat diamond. It contains several smaller stones that add up to about one carat. A single stone is usually priced at far more per carat than several small ones, so check whether a listing refers to one stone or to the total.
How carat became a standard
The word comes from the practice of weighing gems against the seeds of the carob tree, which were called carats in some languages. Before standardization, countries used different carat weights, ranging from roughly 187 to 215 milligrams. The metric carat of 200 milligrams was adopted at the Fourth General Conference on Weights and Measures in Paris in 1907. The United States implemented it on July 1, 1913, and the United Kingdom on April 1, 1914. The result is that a carat today means the same thing in every country.
Why the two spellings exist
Both words trace to the same origin, and "carat" is the older spelling. According to dictionary sources, "karat" was introduced to distinguish gold purity from gemstone weight, and American jewelers have used "karat" for gold since around the mid-1850s. In the United Kingdom and in most of the rest of the world, "carat" is used for both purity and weight.
That produces a practical rule for online shopping:
- In the United States, a listing for gold purity should say karat or K, and a listing for gemstone weight should say carat or ct.
- In listings from other countries, "18 carat gold" is a normal way to say 18K gold, and it does not refer to a gemstone at all.
- If a listing says "18ct gold" or "9ct gold," the "ct" there means purity in the British sense.
- When it is unclear, look at the stamp. A stamp of 750 or 18K tells you the purity regardless of the spelling in the description.
The overlap matters most with imported pieces, and with listings written by sellers who use one spelling for everything. Read the context. If a word is paired with a metal, it is purity. If it is paired with a stone, it is weight.
Common mix-ups
"A 24-carat gold ring." In American usage this should be karat. It means pure gold, which is too soft for most rings, so be careful with claims about a pure gold ring meant for daily wear.
"A 2-karat diamond." Diamonds are weighed in carats. A listing that says karat for a stone is either a spelling slip or a hint the seller is not a specialist, so confirm the weight from a certificate.
"18K means it is better than a 14K with a bigger diamond." They are different questions. Karat tells you the gold content of the metal, and carat tells you the size of the stone.
"More karats means a better ring." Higher karat gold is more valuable by weight and more yellow, but it is softer and scratches and bends more easily. 14K is the most common choice in the American market for everyday jewelry because it balances gold content with durability, according to one retailer's guide. 10K is harder still and lower in gold. 18K is richer in color and softer.
How to use this when you buy
- Check the metal stamp for karat or fineness, and make sure it is a solid gold mark and not a plating mark.
- Check the stone weight in carats, and whether it is one stone or total weight.
- Ask for a grading report on any significant diamond, which states carat weight, color, clarity and cut.
- Do the math on gold content if the piece is priced by weight. Weight times karat divided by 24 gives the gold in grams.
- Ask about both when the piece has a gold setting and a stone. They are separate facts.
Asking sellers on a live stream
A stream lets you ask a seller to show the karat stamp up close, to say what the stone weighs and to confirm whether the stated weight is for one stone or several. On ShopBidz, GG Luxury Revival, from Long Island, New York, sells luxury items and jewelry, and Prettypleaseaz, from Gilbert, Arizona, is another seller you can watch. Ask each to show the stamp, state the karat and describe the stone weight before you bid. If a seller mentions fine jewelry or pearls, our guide to how to tell if fine jewelry and pearls are real covers what to check.
Bottom line
Karat is gold purity, counted in parts out of 24: 24K is about 99.9 percent gold (stamped 999), 18K is 75 percent (750), 14K is about 58.3 percent (585) and 10K is about 41.7 percent (417). Carat is gemstone weight: one carat is 200 milligrams, divided into 100 points of 2 milligrams each. The spelling keeps them apart in the United States, while much of the rest of the world uses "carat" for both, so rely on context and on the stamp. A ring can be 14K and hold a 1-carat diamond, and the two numbers answer different questions. Check both before you pay.