Long Vowels in Hiragana: How to Read and Write ああ, いい, うう, ええ/えい, and おう/おお

In hiragana, a long vowel is one vowel phoneme (sound unit) written across two kana. The vowel quality is held for two timing beats.¹² The o-row is what confuses many beginners: words like おかあさん look the way they sound, but おとうさん is spelled with う even though the final vowel is a long o.³

Overview

Each of the five hiragana vowel rows has a long-vowel pattern fixed by the 1986 Cabinet Notification on Modern Kana Usage (「現代仮名遣い」).³⁴ Four patterns are intuitive: append the matching vowel kana. The o-row needs a separate explanation, plus a closed list of historical exceptions.

This article covers hiragana only. The katakana long-vowel bar (chōonpu, 「ー」) is a separate orthographic system and is treated in the sibling article on long vowels in katakana.

What a long vowel is

A long vowel in Japanese is one vowel phoneme held over two morae. It is not one stretched syllable or a stressed syllable.¹² The mora is Japanese's basic timing unit, and each kana counts as one beat.⁵

In actual sound, a long vowel lasts roughly 2.5 to 3 times as long as a short one. In the sound system, however, it is exactly two morae.² The timing target is "two beats of the same vowel," not "one beat held louder."

Two kana, one vowel sound

A long-vowel word like おかあさん is five morae: お, か, あ, さ, ん, with ん as its own mora. But the あ extending か is heard as one continuous a, not as two distinct vowels.¹²

お母かあさん。²
"Mother (one's own or addressed)."

Why long vowels change meaning

Vowel length is phonemic in Japanese: change the length and you change the word.²⁵ These minimal pairs, pairs that differ in only one sound feature, are why beginners cannot afford to skip the topic.

Short vowel	Long vowel	Gloss difference
おばさん	おばあさん	aunt vs. grandmother2
おじさん	おじいさん	uncle vs. grandfather2
とる	とおる	to take vs. to pass through6
ゆき	ゆうき	snow vs. courage
くろ	くろう	black vs. hardship
ここ	こうこう	here vs. high school

叔母おばさんと祖母おばあさんは違ちがいます。²
"Aunt and grandmother are different (words)."

Length errors flip the word, not just the accent

Saying おじさん when you mean おじいさん is not a foreign-accent slip; it is a different lexical item. The listener will hear "uncle," not a mispronounced "grandfather."²⁵

Hiragana long vowels vs. the katakana bar

In hiragana, a long vowel is written by adding a second kana from the matching vowel row. The o-row has one historically conditioned exception class.³⁶ In katakana, the same length is written with the chōonpu 「ー」 regardless of which vowel is being lengthened.³

The two systems are not interchangeable. Loanwords (gairaigo) written in katakana keep the bar; the same words rewritten in hiragana for a children's book follow the hiragana rules, not the bar. Sibling articles such as Hiragana Chart cover the base kana inventory this rule applies to.

The five long-vowel patterns

The 1986 Cabinet Notification 「現代仮名遣い」 fixes one rule per vowel row in 本文 第1, section 5.³⁴ Four rows take the matching vowel kana. The e-row and o-row each have a small native exception class.

a-row: あ + あ

Rule: an あ-row mora plus あ.³ 第1 5(1) states directly that ア列の長音はア列の仮名に「あ」を添える (an ア-row long vowel adds 「あ」 to an ア-row kana), with no exception class for native vocabulary.³⁴

お母かあさん。³
"Mother."

お婆ばあさん。²
"Grandmother."

ああ。³
"Ah; oh."

i-row: い + い

Rule: an い-row mora plus い.³ 第1 5(2): イ列の長音はイ列の仮名に「い」を添える (an イ-row long vowel adds 「い」 to an イ-row kana).³⁴

お爺じいさん。³
"Grandfather."

お兄にいさん。³
"Older brother."

いい。²
"Good."

u-row: う + う

Rule: a う-row mora plus う.³ 第1 5(3): ウ列の長音はウ列の仮名に「う」を添える (a ウ-row long vowel adds 「う」 to a ウ-row kana).³⁴

夫婦ふうふ。³
"Married couple."

空気くうき。³
"Air."

数字すうじ。³
"Numeral; digit."

e-row: え + い (default), え + え (small native set)

Rule: 第1 5(4) sets エ列の長音はエ列の仮名に「え」を添える (an エ-row long vowel adds 「え」 to an エ-row kana). A 付記 (supplementary note) specifies that words like えいが, とけい, ていねい, へい, めい, れい, せい, and かれい are written with エ列 + い regardless of how they are pronounced.³⁴ The spelling default is therefore えい. ええ appears only in a small native set such as おねえさん and the interjection ええ "yes."³⁴

In standard Tokyo speech, both spellings tend to be realised as [eː], a long e. The NHK reference dictionary records [eː] as the broadcast standard for エイ inside a single morpheme (the smallest meaningful word part), with [ei] appearing across morpheme boundaries or in careful speech.⁷

先生せんせい。³
"Teacher."

映画えいが。³
"Film; movie."

時計とけい。³
"Clock; watch."

お姉ねえさん。³
"Older sister."

ええ。³
"Yes; uh-huh."

o-row: お + う (default), お + お (a closed set)

Rule: 第1 5(5) sets オ列の長音はオ列の仮名に「う」を添える (an オ-row long vowel adds 「う」 to an オ-row kana) as the default.³⁴ A separate provision, 第2 6, lists a small closed set of native words that keep オ列 + お instead.⁶⁴ The full list appears in the next section.

The default おう spelling is pronounced [oː], a long o; the う is not a separate vowel.²

お父とうさん。³
"Father."

学校がっこう。³
"School."

ありがとう。³
"Thank you."

今日きょう。³
"Today."

The お + う = ō convention

What you write vs. what you hear

第1 5(5) prescribes オ列 + う as the default spelling for o-row long vowels, even though the sound is [oː].³⁴ The う is part of the spelling only. It does not surface as a separate [u] in standard speech.² Modified Hepburn writes both おう and おお as ō, since they are the same sound phonemically.¹

The official 第1 5(5) example list gives, among others: おとうさん, とうだい (灯台), わこうど (若人), おうむ, かおう (買おう), あそぼう (遊ぼう), おはよう, おうぎ (扇), とう (塔), はっぴょう (発表), きょう (今日), and ちょうちょう (蝶々).⁴

Do not pronounce the う in おう as a separate vowel

Learners who decode each kana literally will say "o-to-u-san" instead of "otōsan." The う is the second mora of a long o, not an independent vowel.²

Why おう, not おお

The reason the spelling defaults to おう is historical. Late Middle Japanese (roughly 1200 to 1600) collapsed several diphthongs, or vowel glides, into long monophthongs, or single vowel sounds. Twentieth-century orthographic reform then had to decide how to spell the merged sounds.⁸

The 1946 「現代かなづかい」 reform replaced historical kana spellings (旧仮名遣い) with phonetic ones. The 1986 「現代仮名遣い」 refined those rules without changing the long-vowel decisions at issue here.³⁹¹⁰ The 1946 reform spelled all of the merged [oː] outcomes as オ列 + う, regardless of which historical diphthong they came from.¹¹¹⁰

This historical fingerprint explains why everyday おう words look the way they do. おとうさん carries an う that was already there in older spellings. がっこう was historically がくかう (がく + かう, school-place), and ありがとう was ありがたう (有り難う, "(being) hard to come by").¹¹

Reading the う in everyday words

The う in an おう spelling is the second mora of a long o, not an independent [u].² Reading it as a separate vowel is the most common beginner pronunciation error with this spelling.

Hiragana	Kanji	Hepburn	Gloss
おとうさん	お父さん	otōsan	father3
がっこう	学校	gakkō	school3
ありがとう	有り難う	arigatō	thank you3
きょう	今日	kyō	today3
とうきょう	東京	Tōkyō	Tokyo4
ほうほう	方法	hōhō	method4
こうこう	高校	kōkō	high school4
どうぶつ	動物	dōbutsu	animal4

東京とうきょうに行いきます。⁴
"I'm going to Tokyo."

高校こうこうの先生せんせいです。⁴
"(They are) a high-school teacher."

The おお exceptions: a closed list

Why a small group of words keeps おお

「現代仮名遣い」 本文 第2 6 gives an explicit, closed list of words for which オ列 + お is used instead of オ列 + う.⁶⁴ The criterion is historical: these are words whose 旧仮名遣い spelling used オ列 + ほ or オ列 + を, not the あう/あふ pathway that gave the おう default.⁶⁴

The historical spelling already had two separate o-class vowels divided by an h-row or w-row kana whose consonant has since dropped. The reform updated the now-silent ほ or を to お. That left a true OO sequence rather than the AU→ŌU→Ō merger outcome.¹¹

The official wording from 第2 6 says that these words are written by adding 「お」 to an オ-row kana, regardless of whether they are pronounced as an o-row long vowel or as separate vowels like オ・オ or コ・オ: 「これらは，歴史的仮名遣いでオ列の仮名に『ほ』又は『を』が続くものであって，オ列の長音として発音されるか，オ・オ，コ・オのように発音されるかにかかわらず，オ列の仮名に『お』を添えて書くものである。」⁴

The complete おお list from 「現代仮名遣い」 第2 6

The complete list of example words given in 本文 第2 6 appears below with their kanji, gloss, and historical spelling.⁶⁴¹¹

Modern kana	Kanji	Gloss	Historical kana
おおかみ	狼	wolf	おほかみ
おおせ	仰せ	command, statement (honorific)	おほせ
おおやけ	公	public, official	おほやけ
こおり	氷 / 郡	ice / district	こほり
こおろぎ	蟋蟀	cricket (insect)	こほろぎ
ほお	頬 / 朴	cheek / Japanese magnolia	ほほ
ほおずき	鬼灯	Chinese lantern plant	ほほづき
ほのお	炎	flame	ほのほ
とお	十	ten (native counter)	とを
いきどおる	憤る	to be indignant	いきどほる
おおう	覆う	to cover	おほふ
こおる	凍る	to freeze	こほる
しおおせる	し果せる	to carry through to the end	しおほせる
とおる	通る	to pass through	とほる
とどこおる	滞る	to stagnate, be delayed	とどこほる
もよおす	催す	to hold (an event); to feel an urge	もよほす
いとおしい	愛おしい	dear, beloved	いとほしい
おおい	多い	many	おほい
おおきい	大きい	big	おほきい
とおい	遠い	far	とほい
おおむね	概ね	in general, mostly	おほむね
おおよそ	凡そ	roughly, approximately	おほよそ

Compounds and derivatives built on a 第2 6 base inherit the おお spelling. 大阪 (おおさか), 十日 (とおか), 大きな (おおきな), 大いに (おおいに), and 大空 (おおぞら) all trace to the 大, 多, or 十 entries above.⁴¹¹

Memorization strategy

The list is closed at roughly 22 base words plus their compounds, so the practical move is to memorise it as a set rather than try to derive it from rules.⁶⁴ If a long o appears in a word written with 大, 多, 遠, 通, 十, 氷, 凍, 狼, 炎, 公, 仰, 覆, 催, 滞, 憤, 愛 (in 愛おしい), or 概, expect おお. For everything else with a long o, expect おう.⁶

Big numbers, big things: the おお signal kanji

The kanji 大 ("big"), 多 ("many"), 遠 ("far"), 通 ("pass through"), and 十 ("ten") cover most of the おお words a beginner meets. When you see them, default to おお, not おう.⁶

大おおきい家いえです。⁶
"It's a big house."

湖みずうみは遠とおいです。⁶
"The lake is far away."

氷こおりをください。⁶
"Ice, please."

道みちを通とおります。⁶
"(I) go along the road."

十日とおかまで待まちます。⁶⁴
"(I'll) wait until the tenth."

How long vowels behave in real reading

Two morae, one sound

In the sound system, a long vowel is one vowel quality stretched over two morae.¹² In actual duration, it is roughly 2.5 to 3 times as long as a short vowel. For native speakers, the timing target is "two beats of the same vowel."²

This is not English stress: a long vowel is not louder or higher in pitch just because it is long. It is held longer.⁵ A learner who uses English stress to mark length will raise the pitch too much, hold the vowel too briefly, and the word will still sound short.

叔母おばさんは四モーラ、祖母おばあさんは五モーラ。²
"Obasan is four morae; obāsan is five."

Minimal-pair drills

Read each pair aloud at the same pitch. Lengthen only the second vowel of the long form.⁶² All twelve items are real words; there are no nonsense words in the drill.

Short (one beat)	Long (two beats)	Gloss
おばさん	おばあさん	aunt / grandmother2
おじさん	おじいさん	uncle / grandfather2
とる	とおる	to take / to pass through6
ゆき	ゆうき	snow / courage
くろ	くろう	black / hardship
ここ	こうこう	here / high school

Is this kana sequence a long vowel?

When beginners see two vowel kana in a row, they need to know whether the kana form one long vowel or two separate vowels across a morpheme boundary. The decision tree below captures the spelling side of the answer.

Typing long vowels

On a standard romaji IME, the second vowel is typed literally. The IME does not automatically double anything or pick おう vs. おお for you.³ You choose the spelling at the keystroke.

Word	IME input	Result
おかあさん	okaasan	おかあさん3
おにいさん	oniisan	おにいさん3
ふうふ	fuufu or huuhu	ふうふ3
せんせい	sensei	せんせい3
おとうさん	otousan	おとうさん3
おおきい	ookii	おおきい6
とおる	tooru	とおる6

Good to know

The えい / ええ split in casual speech

In spelling, the e-row long vowel takes い by default (せんせい, えいが, とけい) and え in a small native set (おねえさん, ええ).³⁴ In sound, both spellings tend to be realised as [eː] in standard Tokyo Japanese. NHK's reference work records this as the broadcast standard within a single morpheme.⁷

Across a morpheme boundary, or in a carefully pronounced Sino-Japanese compound, [ei] may appear as two distinct vowels.⁷ The contrast learners ask about, 映画 [eːga] vs. the interjection ええ [eː], is about spelling and word history, not sound. The kana differ, but the sound is the same.⁷

Romanisation choices: ō, ou, oo, oh

The same long o can be written four different ways depending on the romanisation system. Learners using mixed-source materials will see all four for the same word.

System	Output for 東京	Output for 大野
Modified Hepburn	Tōkyō	Ōno
Kunrei-shiki	Tôkyô	Ôno
Wāpuro / IME input	Toukyou	Oono
Passport (Japanese government)	Tokyo or Tohkyoh	Ono or Ohno

All four systems describe the same kana. Only the romanised output differs.¹ Modified Hepburn uses a macron ō for both おう and おお, since they are the same sound phonemically.¹

Compound-word long vowels are still long

In 学校 (がっこう), the う is the second mora of こう and belongs to it as a long o.³ Pronouncing each kana separately as ga-k-ko-u is a learner habit, not natural speech.

The same holds for 高校 (こうこう), 方法 (ほうほう), 東京 (とうきょう), and 動物 (どうぶつ). Each o-row + う counts as one long vowel even though the spelling shows two kana.²

学校がっこうに行いきます。³
"I go to school."

Why 1946 left おお alone for a handful of words

The 1946 「現代かなづかい」 reform replaced historical spellings with phonetic ones.⁹¹⁰ Words whose historical spelling was オ列 + ほ (おほ, とほ, こほ) or オ列 + を (とを) already had two separate o-class vowels in their underlying form. The reform updated the now-silent ほ or を to お, yielding おお.⁶⁴¹¹

Words on the あう / あふ / わう / おう pathway (the Late Middle Japanese monophthongisation of /au/ and /ou/⁸) were updated to オ列 + う instead.¹¹¹⁰ The 1986 「現代仮名遣い」 preserved both rules unchanged. That locked in the おお / おう split that learners see today.³⁶

Hiragana long vowels in loanwords are rare

Loanwords are usually written in katakana, with the chōonpu ー marking length (コーヒー, ノート, スーパー).² When a loanword does appear in hiragana, such as in children's books or stylised typography, it follows the hiragana long-vowel rules above, not the bar.³

The katakana long-vowel system is a separate orthographic mechanism, and the sibling article on katakana long vowels covers it in full.

Long vowels are independent of the small つ and yōon

The small っ (sokuon) doubles a consonant; long vowels double a vowel. They occupy different spelling slots and can appear in the same word: 学校 (がっこう) has both a sokuon (っ) and a long o (こう). The sibling articles Small つ (Sokuon) and Yōon: Contracted Sounds in Hiragana cover the consonant-side and palatalised-syllable counterparts. Dakuten and Handakuten, in turn, modify the consonant of a single mora and do not interact with vowel length.

See also

• Why "Tokyo" Is Two Syllables in English and Four Morae in Japanese: Loanwords as a Timing Drill
• The Japanese Vowel Inventory: Five Vowels, Done Right
• Common Romaji Mistakes That Mislead Pronunciation
• The Three Hiragana Spelling Exceptions: は, へ, and を as Particles
• Hiragana, Katakana, or Kanji First? A Beginner's Script Order

References

Footnotes

1. Vance, Timothy J. The Sounds of Japanese. Cambridge University Press, 2008. Chapter 5 (Moras), pp. 56–66, on long vowels as two-mora units. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

2. Wikipedia. "Japanese phonology." Section on vowel length and the mora. https://en.wikipedia.org/wiki/Japanese_phonology ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰ ↩²¹ ↩²² ↩²³ ↩²⁴

3. 文化庁. 「現代仮名遣い」 (昭和61年内閣告示第1号 / 1986 Cabinet Notification No. 1). 本文 第1「原則に基づくきまり」 5(5) (オ列の長音), 5(4) (エ列の長音), 5(1)–(3) (ア列・イ列・ウ列の長音). https://www.bunka.go.jp/kokugo_nihongo/sisaku/joho/joho/kijun/naikaku/gendaikana/honbun_dai1.html ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰ ↩²¹ ↩²² ↩²³ ↩²⁴ ↩²⁵ ↩²⁶ ↩²⁷ ↩²⁸ ↩²⁹ ↩³⁰ ↩³¹ ↩³² ↩³³ ↩³⁴ ↩³⁵ ↩³⁶ ↩³⁷ ↩³⁸ ↩³⁹ ↩⁴⁰ ↩⁴¹ ↩⁴² ↩⁴³ ↩⁴⁴ ↩⁴⁵ ↩⁴⁶ ↩⁴⁷

4. 「現代仮名遣い」 (昭和61年内閣告示第1号), Wikisource transcript of the official text. https://ja.wikisource.org/wiki/現代仮名遣い_(昭和61年内閣告示第1号) ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰ ↩²¹ ↩²² ↩²³ ↩²⁴ ↩²⁵ ↩²⁶

5. Wikipedia. "Japanese language." Section on phonology, mora-timed prosody and phonemic vowel length. https://en.wikipedia.org/wiki/Japanese_language ↩ ↩² ↩³ ↩⁴

6. 文化庁. 「現代仮名遣い」 (昭和61年内閣告示第1号 / 1986 Cabinet Notification No. 1). 本文 第2「表記の慣習による特例」 6 (オ列の仮名に「お」を添えて書く語). https://www.bunka.go.jp/kokugo_nihongo/sisaku/joho/joho/kijun/naikaku/gendaikana/honbun_dai2.html ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰

7. NHK 放送文化研究所 編. 『NHK日本語発音アクセント新辞典』. NHK 出版, 2016. 解説編, 共通語の発音 (treatment of エイ as [eː] in common speech vs. preserved [ei]). ISBN 9784140113455. ↩ ↩² ↩³ ↩⁴

8. Frellesvig, Bjarke. A History of the Japanese Language. Cambridge University Press, 2010. Chapter 8 (Late Middle Japanese phonology), discussion of /au/, /eu/, /ou/ monophthongisation. ISBN 9780521653206. ↩ ↩²

9. Wikipedia. "Historical kana orthography." 1946 現代かなづかい reform, replacement of historical spellings. https://en.wikipedia.org/wiki/Historical_kana_orthography ↩ ↩²

10. 国語審議会. 「現代かなづかい」 (昭和21年内閣告示第33号 / 1946 Cabinet Notification No. 33). The original postwar reform, superseded by ³. Text preserved at https://www.asahi-net.or.jp/~lf4a-okjm/genkan61.htm (commentary with appended 1946 text). ↩ ↩² ↩³ ↩⁴

11. Wikipedia (日本語). 「歴史的仮名遣」. Section listing the あう / あふ / おう / おふ / をう historical spellings that merged into modern オ列 long vowels. https://ja.wikipedia.org/wiki/歴史的仮名遣 ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷