Full Width to Half Width Character Converter, Free

Got a full width character where a half width character is expected — or the other way around? Mixed widths break sorting in contact lists, and email addresses or web forms stop accepting the text. This free online tool converts full-width to half-width, or back, for alphanumerics, katakana, symbols, and spaces, and switches katakana to hiragana on the same screen — all in your browser.

What full-width and half-width characters are

The difference is how much of a square cell each character takes up: the whole cell, or about half of it. Letters and digits (Ａ vs A) and katakana (ア vs ｱ) come in both widths, as do common symbols such as ＠.

In Unicode, full-width alphanumerics occupy U+FF01–U+FF5E, and their half-width counterparts are the ordinary ASCII range U+0021–U+007E. Full-width characters lie outside ASCII, so UTF-8 stores each in 3 bytes, against 1 byte for half-width ASCII. Half-width katakana (U+FF61–U+FF9F) is also outside ASCII, so it takes 3 bytes even though it looks "half-width."

How to convert full-width and half-width characters online

sakuttoAI's converter has two modes: Full-width ⇔ Half-width and Katakana ⇔ Hiragana. Both run in the browser, with no character limit.

Convert full-width characters to half-width, or back

1. Select the "Full-width ⇔ Half-width" tab
2. Choose the direction: full-width → half-width, or half-width → full-width
3. Select which categories to convert — alphanumeric, katakana, symbol, space — any combination of the four
4. Paste or type text in the left text area
5. The converted result appears in real time on the right
6. Click "Copy" to grab the result

Categories can be mixed in any combination, so "half-width alphanumerics only, katakana unchanged" takes just one toggle. Flip the direction and the same selection converts the text back to full-width.

Switch katakana to hiragana with the same tool

1. Switch to the "Katakana ⇔ Hiragana" tab
2. Choose the direction: katakana → hiragana, or hiragana → katakana
3. Paste or type your text and copy the converted result

Converting full-width katakana to half-width katakana

To change only the width of katakana, select just the katakana category and choose a direction. Voiced and semi-voiced katakana convert as pairs that survive a round trip: full-width ガ becomes the two half-width characters ｶﾞ and converts back cleanly. The tool's katakana tables handle the base character and its mark together instead of as separate glyphs.

Why mixed character widths cause real problems

Contact lists and phone numbers

If one entry stores "０３−１２３４−５６７８" in full-width and another stores "03-1234-5678" in half-width, the list treats them as two different numbers, so duplicates slip through and sorting splits them apart. Converting every entry to one width before matching solves it.

Email addresses and URLs need half-width characters

Every character in an address, including the @ sign, must be the ASCII version, not its full-width look-alike. A full-width address or link typically fails, so the message bounces or the page is not found.

Web forms that reject full-width input

Phone number and postal code fields often accept only ASCII digits, so pasting ０３ instead of 03 triggers a validation error. The two look almost alike on screen, so the error is hard to trace back to character width.

Tips for keeping character widths consistent

Store letters and digits as half-width, because email addresses and URLs require it and many forms expect it. For katakana, the right width depends on where the text is going, so find out what the receiving form or database accepts before you convert. Save a copy of the original before a batch conversion and check the output afterward, since input method editors and pasting from some apps can quietly bring full-width characters back.

Summary: convert to one width before you match, search or submit

Full-width and half-width are the same characters shown at two different widths, across alphanumerics, katakana, symbols, and spaces. sakuttoAI's free tool converts either direction, per category, and also switches katakana to hiragana on the same screen. Your text never leaves the browser, and you don't need an account.