Japanese Long Vowels: The Complete Guide
Why is 王 (king) written おう but 大きい (big) written おお? Why is 先生 せんせい but お姉さん おねえさん? And why does katakana use a dash instead? Long vowels are one system with a few spelling rules — this guide covers all of them, plus the listening skill that makes おばさん and おばあさん two different people.
Why Long Vowels Matter
A long vowel in Japanese is simply a vowel held for two beats (two mora) instead of one. Japanese is a mora-timed language: every beat gets roughly equal time, and that extra beat is a real, meaning-carrying unit — not decoration. Get the length wrong and you are saying a different word.
Learners face two separate problems. First, spelling: the same long “oh” sound can be written おう or おお, and the long “eh” can be えい or ええ. Second, hearing: if your native language doesn’t use vowel length this way, your ears filter it out entirely. This guide handles both halves.
Learners who studied with romaji feel the spelling problem most. They see “ō” and have no way to know whether to write おう or おお. The good news: おう is the default for almost every word, and the おお words are a short, fixed list you can memorize in an afternoon.
The おう Rule (the default)
For the vast majority of words — and almost all kango (kanji compounds) — a long “oh” is written おう. Do not read it as “o-u”; it is one long ō.
The おお Exceptions (memorize this list)
A small group of native Japanese words spells the long “oh” as おお. This is a leftover from older kana spelling. There are only a handful in common use — learn them and you are done.
えい vs ええ: The Sister Rule
The e-row works exactly the same way. The long “eh” is almost always written えい — and pronounced as one long ē (not a crisp “e-i”) — especially in kanji compounds:
And just like おお, a tiny set of words spells it ええ — memorize the short list:
Bonus pattern: お姉さん (おねえさん, older sister) sits right next to お兄さん (おにいさん, older brother), which lengthens with いい. Learn the family words as a set.
Katakana: One Mark for Everything — ー
Katakana throws out all the rules above and replaces them with one mark: ー, the chōonpu (長音符) or “long-sound mark.” It means “hold the previous vowel one more beat.” So コーヒー is ko + (hold) + hī: four beats, ko-o-hi-i.
The rule: in katakana, lengthen any vowel with ー — never with あいうえお. Which syllables are long in a loanword follows the original foreign pronunciation, so you learn each word individually — but the mark is always ー. (In vertical text it becomes a vertical line; same job.)
Long vs Short: Minimal Pairs Your Ears Must Learn
Call your friend’s おばあさん (grandmother) an おばさん (aunt / middle-aged lady) and you’ll get a look. These pairs differ only in vowel length — as different to a Japanese speaker as “ship” and “sheep” are to you:
How to Actually Hear It
- Clap the beats. お-ば-さん is 4; お-ば-あ-さん is 5. Clap once per mora and the extra beat becomes physical.
- Say both out loud, back to back. Exaggerate the long one at first — ビーール — then shrink it to normal.
- Train with audio, not text. You already “know” these words by spelling; the skill you need is hearing the length in real time. The JLPT listening section tests exactly this.
Common Mistakes
- Writing おお where おう belongs — e.g. べんきょお ✗ for 勉強 (べんきょう ✓).
- Reading おう as two separate vowels (“o-u”) or えい as a crisp “e-i” instead of one long vowel.
- Forgetting that the おお words exist and “correcting” おおきい to おうきい ✗.
- Leaving the ー out of loanwords: コヒー ✗ instead of コーヒー ✓ — the length change can make the word hard to understand.
- Using a hiragana-style vowel in katakana: コーヒイ ✗ — katakana lengthens with ー, never with かな vowels.
Teacher’s Note
Don’t try to derive the exception words from a rule — memorize the two short lists (おお: 大きい, 多い, 遠い, 通り, 氷, 十, 狼… / ええ: お姉さん, ええ, へえ) and default to おう and えい for everything else. Typing on a computer actually helps: type the reading and watch which spelling converts to the kanji you want. And remember spelling is only half the skill — knowing 王 is written おう only helps if your ears can also tell ō from o. Pair the rules with audio practice and you cover both halves.
Hiragana Guide →
Read every kana
Katakana Guide →
Loanword characters
JLPT Listening Tips →
Train your ears
Hear the difference, don’t just read it
Nihongo Pass adds native audio to every word, so long and short vowels stop blurring together — exactly what you need for the listening section.
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