Inspired by this question, I'm curious as to whether there are similar guidelines for the length of Japanese sentences (Maybe in Japanese clauses are more relevant?) to maximize readability, whether that length is measured by # of kana or # of kanji or some other measure. Sources regarding online writing in blogs and published non-fiction/fiction are particularly interesting.


This site talks about the sentence length using NHK,朝日新聞,日経 as a guideline. The author picked up 5 free article from each company. The methodology is splitting the text by the period symbol and then counting the letters in the sentences.

enter image description here

The sentences from NHK are longer than the sentences from other newspaper companies. NHK could be using different guidelines. Then the author speculates about the case of text by famous novelists.

enter image description here

So, around 20 to 22 words in the sentence is common in those famous novels. Then the author concludes,

結論! 20文字前半がオススメ! これまでの内容をまとめると、「読みやすい文章、気に入られる文章は20文字前半を1文として構成されている」ということみたいです。

All in all, sentences that are easy to read and well liked are made up of around 20 words.

Thanks for mentioning by Chocolate, I mixed up the concept of "line length", "bunsetsu-based line breaking", and "the sentence length" which you are looking for. The following explanation is about line-length and bunsetsu-based layout. It might be redundant but could be of help for you. I will leave it here.

This must be called 「行{ぎょう}長{ちょう}」: "line length". This blog says,


したが、あまり見つけられていません。『デザインの教室 手を動かして学ぶデザ





I was searching a guideline about horizontal writing of Japanese text among books of a design written in Japanese, but I could find little.『デザインの教室 手を動かして学ぶデザイントレーニング』says "approximately from 20 letters to 30 letters" are easy to read, 15 letters are "a little bit short", 40 letters are "can not recommend a lot", 50 letters are "beyond the limit". 『タイポグラフィの基本ルール』says "approximately from 30 letters to 40 letters" are the longest, from 13 letters to 15 letters are the shortest.

According to 文節単位を考慮した文字配置の工夫がもたらす日本語電子リーダーの可読性向上 : Readability of Japanese Electronic Text with Bunsetsu-based Layouts by "大日本印刷株式会社 : Dai Nippon Printing Co., Ltd. / 公立はこだて未来大学 : Future University Hakodate", splitting sentence by bunsetsu-segments makes easier to read. The following is the excerpt from the abstract of the authors.

In Experiment I, we investigate the effectiveness of the layout with bunsetsu-based line breaking. A bunsetsu-based linefeed layout breaks a line between bunsetsu segments, i.e., splitting a bunsetsu segment is prohibited. The reading speed for the bunsetsu-based linefeed layout was faster compared to the conventional text layout with line lengths of 5–40 characters per line.

enter image description here

  • 2
    うーん・・? 「行長」っていうのは、「一行が何文字か」「行頭から行末までの長さ」ってことで、OPの言っている「一文の長さ」「句点(。)までの長さ」「文頭から文末までの長さ」とは違いますよね。
    – Chocolate
    Sep 29 '19 at 0:55
  • @Chocolate 読みやすい文章の長さとは? 一文の長さを調べてみた。 あちゃーじゃあ、これが本題ですね。 Sep 29 '19 at 1:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.