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Full-width / Half-width Converter (Zenkaku / Hankaku)

Conversion direction
What to convert
Output

How to Use

Paste or type text into the input. Pick the conversion direction and select which character categories should be touched: ASCII (letters, digits, punctuation), katakana, and spaces can each be toggled independently. Conversion is lossless for ASCII and spaces; for katakana, dakuten (゛) and handakuten (゜) marks are combined into / expanded from single full-width codepoints as needed.

Zenkaku and Hankaku

In Japanese computing, characters come in two widths. Zenkaku (全角, "full-width") characters occupy two columns of a fixed-width grid and include the native katakana / hiragana / kanji as well as wide copies of ASCII letters, digits, and punctuation. Hankaku (半角, "half-width") characters occupy one column and include normal ASCII plus a separate set of single-column katakana. Inconsistent width is a common source of form-validation and search bugs, which is why explicit conversion tools are widely used.

Conversion Behavior

ASCII: full-width U+FF01..U+FF5E and standard ASCII U+0021..U+007E map 1:1 by a fixed 0xFEE0 offset. Spaces: U+3000 (ideographic space) ↔ U+0020. Katakana: a lookup table converts each full-width katakana to its half-width counterpart; dakuten / handakuten (濁点・半濁点) are decomposed into separate ﾞ / ﾟ marks in the half-width form and re-combined when converting back. Kanji, hiragana, and other scripts are passed through unchanged.

Common Use Cases

  • Normalizing form input so that "Ｔｏｋｙｏ" and "Tokyo" are treated as equal.
  • Cleaning up legacy data exports that mix widths.
  • Preparing CSV / JSON files for systems that strictly require half-width ASCII.
  • Shortening display text by collapsing full-width ASCII into half-width where it fits better.
  • Filling forms that require a specific width (e.g., katakana-only fields in many Japanese websites).

Tips

  • Dakuten (ｶﾞ → ガ) and handakuten (ﾊﾟ → パ) are handled automatically — you don't need to clean up voicing marks by hand.
  • Toggle individual categories off to convert only ASCII, only katakana, or only spaces.
  • Hiragana is NOT converted by this tool; use the Katakana / Hiragana converter first if you also want kana-class conversion.
  • The ideographic space U+3000 is wider than a normal space; converting it to U+0020 can change alignment in monospaced fonts.
  • Round-trip is lossless: Full-width → Half-width → Full-width returns the original text.

Privacy

All conversions happen in your browser. Your text is never sent to any server or stored anywhere.