I had always thought that when you were talking about percentage, fractions, portions, etc., it was always pronounced ぶん. However, I saw its pronunciation listed as on Imabi, a renowned website for self-learners. The likelihood of its being an error was rather low, since the author seemed to really know his stuff, solid.

On Imabi, a couple of examples were given:


*Strangely, MS-IME does not show 八九分 for はっくぶ, I have to type each kanji separately. Could it be due to its not being an idiom?

The first two seem to be 四字熟語, so I would simply assume the pronunciations are not up for discussion. However, what about other combinations, such as 九割九分? According to this native speaker (ID: ywja):

It's either きゅうわりきゅうぶ or くわりくぶ. Personally, I find that きゅうわりきゅうぶ is more common. Also, it sounds more colloquial and casual to my ears, probably because きゅう sounds more casual than く as the reading of 九.

Question #1.
Her/his explanation appears not to be about personal preference, or regional/dialectic difference. If there is indeed room for variation, as this person suggests, what are some common examples (other than ) where multiple readings apply for the sake of nuances? For instance, for 四分, what are the possible readings? よぶ, よんぶ, and/or しぶ? In addition, how does one read 何分, 一分, 三分, 八分, 十分, 百分, and so on?

Unfortunately, that is not all.

First of all, as far as I know, should be read as ぶん for fractions, such as 三分{さんぶん}の一{いち}. The same goes for portions, such as 千人分の生ビール, or 三十年分のビール.

Next, I looked up again in a dictionary, and for this specific pronunciation, , 研究社 listed only one English translation, "percent." The following are all the sample sentences provided:

  1. 銀行は 4 *分の利子で金を貸してくれた。 The bank lent me the money at 4 percent interest.

  2. 日本チームに*分がある勝ちそうだ。 The Japanese team is likely to win.

  3. 今回は我々のほうが*分がいい。 We have an advantage this time.

  4. その仕事は 9 *分どおり済んだ。 The work is 90 percent done.

For 2. & 3., I think is the only possible reading, since only under is this meaning listed. In goo辞書, 1st entry under 分（ぶ）:


Question #2.
For 1. & 4., can you read it as ぶん as well? Moreover, shouldn't it be 9 percent in 4., or 九割?

Again, under 割（り）（わり）, goo辞書 has this definition：

  1. 歩合の単位。1割は10分の1。

And for 分（ぶ）:

  1. 全体を10等分したもの。10分の1相当の量。

  2. 単位の名。㋐割合・利率で、1割の10分の1。全体の100分の1。

I guess one does not simply consult a dictionary, and go "Eureka!"

Question 3.
How does one decide, then, when （一）分 means one-tenth, but not one-hundredth? Moreover, how does one read it? , or ぶん?

長文ですみません… いつも迷惑をかけてばかりんですが…どうぞよろしくお願いいたします！


A1: When 分 means 10%, 一分 ～ 九分 is usually read like いちぶ, にぶ, さんぶ, よんぶ, ごぶ, ろくぶ, ななぶ/しちぶ, はちぶ, きゅうぶ/くぶ. But 九分九厘 is an idiom that is always pronounced くぶくりん. 九割九分 is usually きゅうわりきゅうぶ, but くわりくぶ may not be wrong. 何分 is なんぶ.

A2: These are read as 4分【ぶ】の利子, 分【ぶ】がある, 分【ぶ】がいい, 9分【ぶ】どおり. No exceptions. その仕事は9分どおり済んだ and その仕事は9割済んだ effectively mean the same thing, 90%. See below.

A3: 分 read as ぶ essentially means 10%, not 1%. However, 分 appears to mean 1% if it follows 割, which is another term meaning 10%.

割 means "10% of the entire fraction". 分 on its own works like 割, but 分 also works somewhat like the SI prefix deci-; it's used in combination with another unit and refers to one tenth of it. For example, 一寸五分 (いっすんごぶ) means 1.5 sun (≒4.5 cm), and 37度5分 (さんじゅうななどごぶ) means 37.5 ℃. Likewise, when 割 and 分 are used together, 2割5分 means "2.5割", which is 25%. This explains why both 九割九分 and 九分九厘 mean 99%.

That being said, for historical reasons, 分 means 1% even without 割 in financial contexts and baseball contexts. 4分 (よんぶ) automatically means 4% when you are talking about interest rates and batting averages. Outside of these types of situations, you can assume that 分 read as ぶ means 10% (cf 四分咲き → 40%, 七分袖 → 70%, 五分五分 → fifty-fifty).

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You seem to correctly understand how to read 3分【ぶん】の1, 30年【ねん】分【ぶん】のビール, 2時30分【ぷん】, and so on, so I won't go into detail about them.

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