Carat vs Karat: The Difference Between Gem Weight and Gold Purity

If you have ever seen a "1 carat" ring and an "18 karat" ring and wondered whether they are the same unit, you are not alone. They are not, but they are related. This page covers only the mix-up. For stamp numbers like 585 and 750, use our gold purity numbers guide, and for how karat changes durability, see why gold is soft.

Carat vs Karat at a Glance

The simplest way to remember it is: carat for stones, karat for gold. The table puts the two side by side.

What Is a Carat?

A carat is a unit of mass equal to 200 milligrams, used mainly for gemstones. A diamond retailer's explainer says the weight can be divided into 100 units called points, so a half-carat stone is 100 milligrams and weighs 50 points. An online encyclopedia entry adds that the modern metric carat was adopted in 1907, and before that each country had its own carat, with values ranging from about 187 mg to 216 mg.

Carat is weight, not size. Two stones with the same carat weight can look different in width depending on cut and shape. When you compare stones, compare the millimeter measurements as well as the carat number. Price is not set by carat alone either: color, clarity and cut matter, and so does whether a stone is natural or lab grown. Our lab diamond vs natural diamond guide explains how those differ.

What Is a Karat?

Karat describes gold purity as the number of parts of gold in 24. The explainer states it directly: 24K contains 24 of 24 parts gold, an 18K necklace is 18 of 24 parts, and a 14K bracelet has 14 of 24 parts. Turn that into a percentage by dividing by 24 and you get the figures below, which are our calculation from the parts-out-of-24 rule.

The rest of the metal in a lower karat piece is other metals mixed in to add strength, so a lower karat is not "fake", it is a different alloy. If you are choosing between karats for a ring or necklace, our 10K vs 14K vs 18K gold comparison covers cost and wear.

Why Do People Confuse Carat and Karat?

They sound the same and come from the same root. The encyclopedia traces carat through Italian carato and Arabic qirat to a Greek word for the carob seed, and says carob seeds were long used to weigh jewelry. It also says gold fineness in carats comes from the same historical system, with refiners' carats for gold descending from the carat as a fineness measure. So the words were once one idea, and they split into a weight unit and a purity unit.

Is It Karat or Carat for Gold?

In US usage it is karat for gold and carat for stones, but you will see "carat" used for gold purity too. Several of the jeweler and finance pages we read use "24-carat" and "22-carat gold" for purity, so a listing that says "18 carat gold" is describing purity, not weight. We did not find a source that explains why the spellings split, so we will not guess at the history. The practical rule: if the number is 24 or lower and the item is metal, it is purity; if it is a stone, it is weight.

Why is karat abbreviated with a K?

K is simply the first letter of the "karat" spelling, and "ct" is the usual abbreviation for carat. You will see 18K, 18kt and 18ct on gold, depending on the market, and all three mean 18 parts in 24.

How to Read a Jewelry Listing

A listing for a gold ring set with a diamond will often carry both words, so the order helps: the metal gets the karat, the stone gets the carat. "14K gold, 0.50 ct diamond" means a 14-parts-in-24 gold band holding a stone that weighs 100 milligrams. Gold plating is a separate matter: a plated piece can be marked with a karat for the plating layer, but the piece underneath is another metal. See is gold plated jewelry real gold.

Where AJLuxe Fits

AJLuxe jewelry does not use carat or karat as a selling point. Our pieces are 925 sterling silver or 316L stainless steel with 18K gold plating, and the stones are cubic zirconia or simulated stones, not weighed natural gems. Where "18K" appears on one of our product pages it describes the plating, and the piece is not solid gold. Browse the gold plated jewelry collection or the stud earrings, and compare stones in cubic zirconia vs diamond.

Frequently Asked Questions

Is it 24 karat or carat?

For gold purity, the US spelling is karat, so 24 karat gold is pure gold. Some sources and markets write 24-carat for the same thing, so treat both as purity when the item is metal.

Which is correct, karat or carat?

Both are correct, for different things. Carat measures gemstone weight and karat measures gold purity in US usage, although some sources use carat for gold as well.

What is 75% gold called?

75% gold is 18 karat, written 18K or stamped 750. It is 18 parts gold out of 24, with the remaining 6 parts other metals.

Why is 1 carat so expensive?

Carat is only the weight of the stone, and price depends on more than weight: cut, color, clarity and whether it is natural or lab grown also set it. We do not quote a price here because it varies widely by stone.

How many milligrams is one carat?

One carat is 200 milligrams, divided into 100 points of 2 milligrams each, according to a reference encyclopedia.

Does a higher carat mean a bigger diamond?

It means a heavier stone, not necessarily a wider one. Two diamonds of the same carat weight can look different in size depending on cut and shape.

Is 18K gold the same as 18 carat gold?

Yes in terms of purity: both mean 18 parts gold in 24, or 75%. The spelling differs by market.

Sources

Compared for this page, all read on 8 October 2026: a diamond retailer explainer on carat and karat (200 mg, points, parts out of 24), an online encyclopedia entry on the carat unit (1907 metric carat, word origin, gold fineness history), and a jeweler reference page on 999 gold (use of the term 24-carat). Product details come from ajluxe.com product pages.

Written by AJLuxe Team. Last updated: October 2026

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