Full-width / Half-width Converter (Zenkaku / Hankaku)
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.
FAQ
What actually distinguishes full-width from half-width?
Full-width (zenkaku) characters take up two columns of a fixed-width grid and include Japanese kana/kanji plus wide copies of ASCII letters, digits, and punctuation. Half-width (hankaku) characters take one column and cover normal ASCII plus single-column katakana. Mismatched widths often cause form-search and validation bugs, which is why explicit conversion is needed.
Is the text I enter sent to a server?
No. Every conversion runs entirely in your browser, and your text is never sent to or stored on any server. You can safely convert data that contains personal information.
Can I convert ASCII, katakana, and spaces separately?
Yes. Each of the three categories can be toggled on or off independently, so you can convert only ASCII, only katakana, or only spaces as needed.
Are half-width katakana with dakuten or handakuten converted correctly?
Yes. Cases like ｶﾞ → ガ and ﾊﾟ → パ are handled: the separate half-width dakuten (ﾞ) and handakuten (ﾟ) marks are combined into a single full-width character, and decomposed again in the reverse direction. You don't need to fix voicing marks by hand.
Are hiragana and kanji also converted?
No. The tool only touches ASCII, katakana, and spaces; hiragana, kanji, and other scripts are passed through unchanged. If you need katakana ↔ hiragana conversion, use the dedicated converter for that.