Translation guide
The unit of weight for gemstones and pearls, equal to 200 milligrams.
このダイヤモンドは何カラットですか？
How many carats is this diamond?
Expressing the weight of a gemstone or pearl in carats.
The standard loanword for 'carat' used in jewelry contexts. It is the most common and natural way to express this concept in Japanese.
このダイヤモンドは2カラットです。
This diamond is 2 carats.
Sometimes written with the kanji 斤, but this is rare and mostly seen in older or technical texts. The katakana form is overwhelmingly preferred.
In English, 'carat' (gem weight) and 'karat' (gold purity) are distinct. In Japanese, both are expressed as カラット, but context usually makes the meaning clear. For gold purity, you may also see 'K' used (e.g., 18K).
18金
18-karat gold
5斤のルビー
a 5-carat ruby