What is the most appropriate way to indicate a long vowel in Katakana?


I know that often, when rendering a long vowel in Katakana, a hyphen is used.

For example, the Katakana rendering of the English word "coat" is often shown
as コート .

I have seen both "ko-to" and "kooto" as the Romaji rendering of this word, and
I wonder: could コオト also be a correct Katakana rendering? ... or also maybe
even コウト ?

This question isn't specfic only to コート . I know that there is more than one
way to render long vowels in Katakana. I just want to know which is the
_**preferred**_ way to render these Katakana long vowels.

ありがとうございます




What I was taught ages ago, and what seems to be borne out by the things I've
read and pored over through the years, modern katakana uses the
[長音符【ちょうおんぷ】](https://ja.wikipedia.org/wiki/%E9%95%B7%E9%9F%B3%E7%AC%A6)
(literally, "long sound mark") or 伸【の】ばし ("lengthener") to indicate long
vowels. In horizontal text, this looks a bit like an [em
dash](https://en.wikipedia.org/wiki/Dash#Em_dash) or even an _ichi_ kanji
[一](https://en.wiktionary.org/wiki/%E4%B8%80#Japanese), while in vertical
text, it's a vertical line that is clearly distinct from a horizontal hyphen
or _ichi_.

That said, there are special cases even in modern use where you might see
something romanized as _kō_ spelled in katakana as コウ, particularly certain
dictionary publications that use katakana to spell out the
[_on'yomi_](https://en.wiktionary.org/wiki/%E9%9F%B3%E8%AA%AD%E3%81%BF#Japanese)
for kanji. And historically, starting (I think) from probably some time in the
Meiji or Taishō eras and up until World War II, katakana was the standard kana
form for regular official published texts -- _not_ hiragana.

So in any modern context, for words like _kōto_ , you will almost always see
コート. You might rarely encounter コオト, but that's because the author is trying
to be cute or stylistically distinct somehow, kinda like English _nite_. --
the "regular" way to spell it is with the 長音符. I don't think you'll ever see
コウト, since this is a borrowed word that has never had an "u". ( _On'yomi_ with
_o_ + _u_ in kana are pronounced nowadays as one long _ō_ , but historically,
these did actually have that _u_ sound.)




What I was taught ages ago, and what seems to be borne out by the things I've
read and pored over through the years, modern katakana uses the
[長音符【ちょうおんぷ】](https://ja.wikipedia.org/wiki/%E9%95%B7%E9%9F%B3%E7%AC%A6)
(literally, "long sound mark") or 伸【の】ばし ("lengthener") to indicate long
vowels. In horizontal text, this looks a bit like an [em
dash](https://en.wikipedia.org/wiki/Dash#Em_dash) or even an _ichi_ kanji
[一](https://en.wiktionary.org/wiki/%E4%B8%80#Japanese), while in vertical
text, it's a vertical line that is clearly distinct from a horizontal hyphen
or _ichi_.

That said, there are special cases even in modern use where you might see
something romanized as _kō_ spelled in katakana as コウ, particularly certain
dictionary publications that use katakana to spell out the
[_on'yomi_](https://en.wiktionary.org/wiki/%E9%9F%B3%E8%AA%AD%E3%81%BF#Japanese)
for kanji. And historically, starting (I think) from probably some time in the
Meiji or Taishō eras and up until World War II, katakana was the standard kana
form for regular official published texts -- _not_ hiragana.

So in any modern context, for words like _kōto_ , you will almost always see
コート. You might rarely encounter コオト, but that's because the author is trying
to be cute or stylistically distinct somehow, kinda like English _nite_. --
the "regular" way to spell it is with the 長音符. I don't think you'll ever see
コウト, since this is a borrowed word that has never had an "u". ( _On'yomi_ with
_o_ + _u_ in kana are pronounced nowadays as one long _ō_ , but historically,
these did actually have that _u_ sound.)

