How to use the fullwidth and halfwidth character converter
- Paste your text into the box.
- Choose a direction: to half width or to full width.
- Tick the kinds of character you want to change: letters, digits, punctuation and symbols, spaces and katakana. Anything you leave unticked stays as it is.
- Read the counts of changed characters, then copy or download the converted text.
Formula
Full width ASCII U+FF01 to U+FF5E = ASCII U+0021 to U+007E + 0xFEE0
Ideographic space U+3000 = space U+0020
Half width katakana U+FF61 to U+FF9F = full width katakana
ｶ + ﾞ (U+FF76 and U+FF9E) = ガ (U+30AC)
The sound marks ﾞ (U+FF9E) and ﾟ (U+FF9F) combine with the letter before them when you convert to full width, and a voiced full width katakana splits into the letter and the mark going the other way.
A mixed line
The line "Ｈｅｌｌｏ Ｗｏｒｌｄ！ １２３" holds full width letters, an ideographic space, an exclamation mark and digits. Converted to half width with every box ticked it becomes "Hello World! 123".
The half width katakana line "ｶﾞｷﾞｸﾞ ｱｲｳ ﾊﾟｰﾃｨｰ" becomes "ガギグ アイウ パーティー" when converted to full width, with each sound mark joined to its letter. With the spaces box ticked, the spaces also become ideographic spaces.
Why two widths exist
Older Japanese, Chinese and Korean computer systems drew characters on a grid where Latin letters took one cell and ideographs took two. Unicode kept both forms of the Latin letters, digits, punctuation and katakana so text could round-trip. Today full width letters and digits still show up in forms, in copied web text and in files from older systems, and they do not match the same letters in plain ASCII when you search, sort or compare.
Converting to half width fixes searches and database matches for letters, digits and symbols. Converting to full width is useful when a form or a layout expects uniform widths in East Asian text.
What stays as it is
Only the characters in the ticked groups change. Kanji, hiragana and full width katakana in a half width conversion of letters only are left alone, and so are characters with no counterpart in the other width, such as most accented letters. A few punctuation marks have no half width form either.
Half width katakana are narrow and are discouraged in many systems because some fonts and encodings handle them poorly. If you only need a clean search key, converting to half width for letters and digits and to full width for katakana is a common choice.
Assumptions and limits
- The ASCII range maps by a fixed offset. The fullwidth signs cent, pound, not, broken bar, yen and won are included under symbols.
- Katakana mapping follows the Unicode compatibility decomposition, so each pair is the one Unicode defines.
- The sound marks join only when the letter before them has a voiced or semi-voiced form.
- Nothing is uploaded. The text stays in your browser and up to 200,000 characters are read.
Frequently asked questions
Is this the same as NFKC normalization?
It is narrower. NFKC also changes many other compatibility characters, while this tool converts only the width forms you tick.
Why did a mark stay on its own after converting?
A sound mark joins only the letter right before it. If that letter cannot take a mark, or something else sits between them, the mark stays separate.
Can I convert only digits?
Yes. Untick the other groups and only digits change.
What happens to Korean text?
Half width Hangul is not converted by this tool. Only letters, digits, symbols, spaces and katakana are handled.