Translation guide
The quality of being firm, solid, or difficult to bend, cut, or break. In Japanese, the most common word is 硬さ (katasa), but the choice of kanji and word depends on the type of hardness and context.
Describing how hard or firm a substance or object is (e.g., metal, wood, food).
The most general term for physical hardness, used for materials like metal, wood, plastic, and also for firm foods. The kanji 硬 implies rigid, stiff hardness.
Please measure the hardness of this metal.
この肉は硬さがちょうどいい。
This meat has just the right firmness.
Technical term for hardness, often used in scientific or industrial contexts (e.g., Mohs hardness, water hardness).
ダイヤモンドの硬度は10です。
The hardness of diamond is 10.
水の硬度を調べる。
Check the hardness of the water.
Used for hardness in the sense of being firm, solid, or tightly packed, often for food texture (e.g., tofu, jelly) or soil. The kanji 固 implies solidity and stability.
この豆腐は固さが足りない。
This tofu isn't firm enough.
地面の固さを確認する。
Check the hardness of the ground.
Referring to the level of difficulty of a task, problem, or the strictness of a person.
The most direct translation for 'hardness' as difficulty. Used for problems, exams, situations.
この問題の難しさに驚いた。
I was surprised by the hardness of this problem.
試験の難しさは年々増している。
The hardness of the exam is increasing year by year.
Used for strictness or severity, such as of a person, rule, or condition. Implies harshness rather than intellectual difficulty.
Specifically referring to mineral content in water.
The standard term for water hardness. Often used in the phrase 水の硬度.
この地域の水は硬度が高い。
The water in this area has high hardness.
硬さ (katasa) is the most common for rigid hardness (metal, wood). 固さ (katasa) is for firmness/solidity (tofu, soil). 硬度 (koudo) is technical (Mohs scale, water hardness). In many everyday contexts, 硬さ is the safe choice.
English 'hardness' can mean difficulty, but Japanese 硬さ only refers to physical rigidity. Use 難しさ (muzukashisa) for difficulty.
The hardness of his coaching is famous.
自然の厳しさを感じる。
Feel the hardness of nature.