How to convert Japanese characters into roman characters when you accidentally type an English word with Japanese input turned on (on Windows)

Press F10 to revert it to Latin script. There is also F9, but this will result in full-width characters, which is usually not appropriate when typing English.

The function keys F6-F10 are used to convert input to various formats:

• F6: convert to Hiragana

  ホワイト → ほわいと

• F7: convert to full width Katakana

  ほわいと → ホワイト

• F8: convert to half width Katakana. Probably not desired

  ホワイト → ﾎﾜｲﾄ

• F9: convert the current input to full width romaji. Probably not desired, too. Press again for all-capitals, then again for proper noun capitalization:

  ホワイト → ｈｏｗａｉｔｏ → ＨＯＷＡＩＴＯ → Ｈｏｗａｉｔｏ

• F10: convert to half width romaji. Press again for all-capitals, and again for proper noun capitalization:

  ホワイト → howaito → HOWAITO → Howaito

If you forget the above then just use Windows+forward slash (/) which is the shortcut for "Begin IME reconversion".

If you only want to convert the next input to romaji you can just type a capital character.

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Some other useful shortcuts for typing Japanese on English keyboard

• Ctrl+Caps Lock: switch to Hiragana
• Alt+Caps Lock: if in alphanumeric mode change to Hiragana, then switch to Katakana
• Shift+Caps Lock: switch between full-width Hiragana ↔ full-width alphanumeric (romaji)
• Alt+` (Grave Accent/Backtick): switch between kana ↔ half-width alphanumeric (romaji)
• Alt+Shift: switch between languages (IMEs)