Long Vowels in Hiragana

In Japanese, holding a vowel for two beats instead of one can change the word entirely. おばさん (obasan) is "aunt"; おばあさん (obāsan) is "grandmother." The difference is a single extra beat of the a vowel — nothing else. Because this length is phonemic (meaning-bearing, not decorative), hiragana has a precise system for writing it. This page teaches that system, including the two spelling conventions that trip up every beginner: えい and おう.

The basic idea: add a vowel kana

Hiragana writes a long vowel by adding a second vowel kana after the first. A long vowel counts as two moras — two beats of equal length (see The Mora). For three of the five vowels, the spelling is exactly what you would guess:

So far, so simple. The complications begin with e and o.

The え-row twist: ええ vs えい

You would expect a long e to be written えー... ええ. And for a handful of words it is. But for the overwhelming majority of Japanese words, a long e sound is spelled えい — that is, え followed by い, not another え.

Here is the distinguishing insight. Even though せんせい is written with い, in normal speech it is pronounced as a long ē — "sensē," not "sen-say." The い is not a separate i vowel you glide to; it is the spelling convention Japanese uses to mark a lengthened e. This is why Hepburn romaji writes sensei but your ear hears sensē.

The お-row twist: おお vs おう

Long o follows the same logic, and it is even more common. For most words, a long o is spelled おう — お followed by う, not another お.

Again, the う does not add a separate u sound. ありがとう is pronounced arigatō — a long final o — not "arigato-oo." The う simply marks the length of the o.

The exceptions: words spelled with doubled kana

A small but frequent set of words breaks the えい/おう pattern and uses doubled kana (ええ, おお) instead. There is no sound difference — おおきい and a hypothetical おうきい would sound identical — so these simply have to be memorized. Fortunately the list is short and the words are extremely common:

Note that おねえさん (older sister) is the odd one out of the family: おにいさん (brother, ii → いい) and おとうさん (father, ō → おう) follow the regular patterns, but おねえさん takes doubled ええ.

Why this matters: length is phonemic

If you are tempted to treat vowel length as a minor detail, these minimal pairs will change your mind. Each pair differs only in the length of one vowel, and each means something completely different:

Call your friend's aunt おばあさん and you have just called her a grandmother — a memorable social mistake. This is why length cannot be treated as optional.

Common mistakes

The most common English-speaker errors are two: ignoring length entirely (saying obasan and obāsan the same way), and reading おう as a literal 'o-u' diphthong ("ari-gato-oo") instead of a single held ō. Both come from English having no habit of doubling a vowel's duration to change meaning. Train your ear on the minimal pairs above and hold the long vowel a genuine two beats.

Key takeaways

• Hiragana writes long vowels by adding a vowel kana; a long vowel is two moras.
• あ/い/う simply double: ああ (ā), いい (ī), うう (ū).
• Long e is normally spelled えい (せんせい, pronounced sensē); long o is normally spelled おう (がっこう, ありがとう).
• A short list of exceptions uses doubled kana: おおきい, とおい, こおり, おおい, とおる, おねえさん.
• Vowel length is phonemic — おばさん ≠ おばあさん. Never skip it.

Katakana handles long vowels completely differently, using a single long stroke — see The Chōonpu (ー). For the pronunciation side, see Long Vowels and Vowel Length.