What are full-width and half-width characters?

Full-width (zenkaku) characters occupy the same square cell as a kanji, while half-width (hankaku) characters take half that width. Japanese text often mixes full-width Latin letters and digits with normal half-width ASCII, which causes inconsistent data.

How does the ASCII conversion work?

Full-width ASCII lives in the Unicode block U+FF01 to U+FF5E, which sits exactly 0xFEE0 above the matching plain ASCII codes U+0021 to U+007E. Converting is a fixed code-point shift in either direction, with the full-width space U+3000 mapped to and from a normal space.

What about half-width katakana?

When converting to full-width you can also map half-width katakana (U+FF61 to U+FF9F) to standard full-width katakana. The tool recombines a half-width dakuten or handakuten that follows a base kana, so ｶﾞ becomes ガ and ﾊﾟ becomes パ.

Why normalise width before storing data?

Search, sorting, and de-duplication treat Ａ and A as different characters, so width inconsistency causes missed matches and duplicate records. Normalising ASCII to half-width and katakana to full-width gives a single canonical form for indexing.

No. All conversion happens in your browser using code-point arithmetic and a built-in katakana table. Nothing you paste is sent to a server.

Japanese Full-Width / Half-Width Converter

Email me this result

Get this tool's output sent to your inbox, plus one useful tool a week. No spam, unsubscribe any time.

Japanese text frequently mixes full-width (zenkaku) and half-width (hankaku) characters, which breaks search and data consistency. This converter normalises ASCII and katakana between the two widths using the correct Unicode mappings.

How it works

Full-width ASCII is a clean offset of plain ASCII, so the conversion is arithmetic rather than a lookup table:

full-width ASCII  U+FF01..U+FF5E  =  ASCII U+0021..U+007E + 0xFEE0
full-width space  U+3000          <-> half-width space U+0020
half-width katakana U+FF61..U+FF9F -> full-width katakana (table)
   ｶ + ﾞ (dakuten)    -> ガ
   ﾊ + ﾟ (handakuten) -> パ

To go from full-width to half-width, subtract 0xFEE0; to go the other way, add it. For half-width katakana the tool uses a mapping table and looks ahead one character to recombine a trailing voiced or semi-voiced mark into the single composed kana.

Tips and example

Ｈｅｌｌｏ　２０２６ converts to Hello 2026, and half-width ｶﾞｲﾄﾞ converts to ガイド. Normalise ASCII to half-width and katakana to full-width before indexing user input, so that Ａ and A, or ﾃｽﾄ and テスト, are treated as the same string. Apply the same normalisation to both the stored data and the query.