Translation guide
Expressing 'half the amount' in Japanese depends on what is being halved: a quantity, a price, a portion, or a comparative degree. The most common pattern uses 半分 (はんぶん) with the particle の or as a standalone noun. For countable items, 半数 (はんすう) is used. In comparative contexts, 半分の～ or ～の半分 is natural.
Expressing that something is half of a whole amount, size, or portion.
The most common and versatile word for 'half'. Can be used as a noun or with の to modify another noun.
ケーキを半分に切ってください。
Please cut the cake in half.
この量の半分で十分です。
Half of this amount is enough.
Pattern to say 'half of something'. Place the thing being halved before の半分.
給料の半分を貯金しています。
I save half of my salary.
Specifically means 'half price'. Used in commercial contexts.
この商品は半額です。
This item is half price.
Means 'half the number' for countable things like people or items.
参加者の半数が女性でした。
Half of the participants were women.
Expressing that something is half as much in degree, intensity, or comparison.
Used to say 'half the (noun)' where the noun is an abstract quantity like size, length, or effort.
半分の時間で終わらせた。
I finished it in half the time.
半分の努力で同じ結果が出せた。
I got the same result with half the effort.
Pattern for 'half the (noun) of (something)'. More explicit comparison.
この箱はあの箱の半分の大きさです。
This box is half the size of that box.
Specifically referring to a monetary amount being halved.
Standard term for 'half price'. Common in stores and advertisements.
今日は全品半額です。
Everything is half price today.
Literally 'half the price'. More colloquial than 半額.
これ、半分の値段で買ったよ。
I bought this for half the price.
Use 半分 for uncountable amounts, portions, or abstract halves. Use 半数 for countable numbers of people or things.
水の半分を飲んだ。
I drank half of the water.
学生の半数が欠席した。
Half of the students were absent.
English 'half the amount' often translates simply as 半分. Adding 量 (りょう) is usually unnecessary and can sound unnatural unless emphasizing a measured quantity.