Translation guide
In Japanese, expressing 'fraction' depends on whether you mean a mathematical fraction, a small part of something, or a tiny amount. The most common everyday word for a small part is 一部 (ichibu), while mathematical fractions use specific terms like 分数 (bunsū).
To refer to a part of a whole, often a small amount, in general contexts.
The most common and versatile word for 'a part' or 'a fraction' of something. It can be used in both concrete and abstract contexts.
I only remember a fraction of the story.
I save a fraction of my income.
Emphasizes 'one part' or 'a portion'. Slightly more explicit than 一部.
I ate only a fraction of it.
Means 'a tiny amount' or 'only a fraction'. Often used adverbially as わずかに.
It finished in a fraction of the time.
To refer to a numerical fraction in mathematics or exact proportions.
The standard term for a mathematical fraction. Used in arithmetic and math contexts.
Calculating fractions is difficult.
To emphasize an extremely small quantity, often in scientific or precise contexts.
To refer to a fraction as a breaking or dividing, often in technical or literary contexts.
分数 (bunsū) specifically means a mathematical fraction like 1/2. Using it to mean 'a small part' in everyday speech will sound unnatural. Use 一部 (ichibu) instead.
A fraction of the people agreed.
一部 (ichibu) and 一部分 (ichibubun) are often interchangeable, but 一部分 can sound slightly more emphatic or specific about 'one part'. 一部 is more common in everyday speech.
I saw the whole thing. (literally 'from one part to the end')
Only a fraction of the students passed the exam.
He completed the work in a fraction of the usual time.
1/2 is a fraction.