Full-width / Half-width Converter — Numbers, Letters & Katakana

Convert numbers, letters, katakana and spaces between full-width and half-width forms, all at once. Handles half-width katakana voiced marks correctly (e.g. ｶﾞ → ガ). Everything runs in your browser — nothing is ever sent anywhere.

Your text

Your text is processed entirely in your browser and is never sent anywhere.

Conversion direction

Convert to half-widthConvert to full-width

Character types to convert

Digits (0-9 / ０-９)Letters (A-Z, a-z / Ａ-Ｚ, ａ-ｚ)KatakanaSpaces

Result

How to use

Paste or type your text into the box above.
Choose "Convert to half-width" or "Convert to full-width", and check the character types you want converted (digits, letters, katakana, spaces).
The "Result" box updates instantly. Use "Copy result" to paste it wherever you need it.

How it works

Converting digits and letters

Half-width (ASCII) digits and letters and their full-width counterparts always sit at a fixed offset (+0xFEE0) in Unicode. This tool uses that fixed offset to convert only the matching characters.

Converting spaces

Half-width and full-width (U+3000) spaces are converted one-to-one. Because this doesn't follow the same offset rule as digits and letters, it's handled as a separate, dedicated rule.

Converting katakana (voiced-mark handling)

Half-width katakana (like ｱｲｳ) and full-width katakana (アイウ) can't be converted with a simple offset, so this tool uses a lookup table instead.

The part that needs special care is voiced and semi-voiced marks. In half-width katakana, "ガ" (ｶ with a voicing mark) is written as two characters: ｶ followed by the half-width voicing mark ﾞ. When converting half-width to full-width, this tool correctly merges that pair into the single full-width character ガ. Converting the other way, ガ is correctly split back into ｶﾞ.

If a voicing mark follows a character that has no voiced form (like ｱ), or appears on its own at the start of text, it isn't merged — it's converted to the standalone full-width mark instead.

Characters with no half-width katakana equivalent — kanji, hiragana, and small katakana like ヵ or ヶ — are left unconverted.

What's left unconverted

Any character that isn't a digit, letter, katakana character, or space — punctuation, kanji, hiragana, and so on — passes through unchanged regardless of which options are selected.

FAQ

Is my text sent anywhere?

No. All processing happens entirely inside your browser, and nothing is transmitted to a server. Once the page has loaded, it keeps working even offline.

Does it handle half-width katakana voicing marks correctly (like ｶﾞ)?

Yes. A half-width base character followed by a voicing mark (ｶ + ﾞ) is correctly merged into a single full-width character (ガ). Semi-voiced marks work the same way (ﾊﾟ → パ). Converting the other direction splits full-width voiced characters back into the correct half-width pair.

Can I convert just one type of character, like only digits?

Yes. Uncheck the character types you don't want touched under "Character types to convert". To convert only digits, for example, uncheck letters, katakana, and spaces.

Does it convert kanji, hiragana, or punctuation?

No. This tool only handles digits, letters, katakana, and spaces. Any other character — kanji, hiragana, punctuation, and so on — always passes through unchanged.

What happens with full-width characters that have no half-width equivalent?

Characters like the small katakana ヵ or ヶ have no half-width form, so converting to half-width leaves them unchanged.