Full-Width & Half-Width Converter | Free Tool for Batch Character Conversion

Need to fix full-width email addresses to half-width? Want to standardize a list of names where katakana is a mix of half-width and full-width? Inconsistent character widths cause data mismatches and errors. This guide explains how to batch convert between full-width and half-width characters using a free online tool.

What Are Full-Width and Half-Width Characters?

In East Asian computing (Japanese, Chinese, Korean), characters come in two widths: full-width and half-width. This system dates back to early CJK computing, where monospaced fonts needed two character cells for wide characters (kanji, hiragana) and one cell for narrow ones (ASCII letters). Today, both forms exist in Unicode and can be converted between.

In Japanese text, hiragana and kanji are always full-width, but alphanumeric characters, katakana, and some symbols exist in both forms — and that's where mixing occurs.

How to Use the Conversion Tool

Full-Width ⇔ Half-Width Conversion

1. Select the "Full-width ⇔ Half-width" tab
2. Choose the direction (full-width → half-width or half-width → full-width)
3. Select which character types to convert (alphanumeric, katakana, symbols, spaces)
4. Paste or type text in the left text area
5. The converted result appears in real time on the right
6. Click the "Copy" button to grab the result

You can select multiple conversion targets, so requests like "only convert alphanumeric to half-width" or "only standardize katakana to full-width" are easy to handle.

Katakana ⇔ Hiragana Conversion

1. Switch to the "Katakana ⇔ Hiragana" tab
2. Choose the direction (katakana → hiragana or hiragana → katakana)
3. Enter or paste your text
4. Copy the converted result

When You Need Full-Width / Half-Width Conversion

Database and Contact List Cleanup

When phone numbers in a customer list mix "０３−１２３４−５６７８" (full-width) with "03-1234-5678" (half-width), search and sorting don't work properly. Standardizing to half-width ensures data consistency.

Email Addresses and URLs

Email addresses and URLs must be in half-width characters to function. Submitting a full-width address causes delivery errors or broken links.

Web Form Input

Many web forms require phone numbers and postal codes in half-width. Submitting full-width characters triggers validation errors.

Document Formatting Standards

In business documents and web content, the standard practice is to use half-width for alphanumeric characters. Mixing full-width and half-width makes text harder to read and reduces searchability.

Comparison with Excel's Full-Width / Half-Width Conversion

Excel can also convert character widths, but the workflow differs from an online tool.

For quick conversion of small text, use the online tool. For bulk processing of spreadsheet data, use Excel functions.

Tips for Standardizing Character Widths

Use Half-Width for Alphanumeric Characters

In Japanese documents, "half-width for alphanumeric" is the de facto standard. Full-width letters (Ａ, １) are visually awkward and don't work in email addresses or URLs.

Use Full-Width for Katakana

Half-width katakana (ｱｲｳ) is difficult to read and can cause encoding issues. For websites and email, always use full-width katakana.

Save Original Data Before Converting

Batch conversion is convenient but can produce unintended results. Always save a backup of your text before converting.

Frequently Asked Questions (FAQ)

Is my input text sent to a server?

No. All processing happens in your browser. Your input text is never sent to any external server, so you can safely use it with personal or confidential information.

Can I choose which character types to convert?

Yes. For full-width ⇔ half-width conversion, you can freely combine four categories: alphanumeric characters, katakana, symbols, and spaces. For example, you can convert only alphanumeric characters to half-width while leaving katakana unchanged.

Can I convert between katakana and hiragana?

Yes. Switch to the "Katakana ⇔ Hiragana" tab for bidirectional conversion. Voiced marks, semi-voiced marks, and small characters are all converted accurately.

Are half-width katakana with voiced marks (ｶﾞ, ﾊﾟ, etc.) handled correctly?

Yes. Half-width katakana voiced marks are represented as two characters (e.g., ｶﾞ = ｶ + ﾞ), but the tool recognizes them correctly and converts to full-width "ガ".

Does it work on mobile?

Yes. It works in any browser on iPhone or Android. Just paste text and the converted result appears instantly.

Summary

Inconsistent full-width and half-width characters cause data mismatches, system errors, and formatting issues. sakutto's conversion tool lets you select and batch convert alphanumeric characters, katakana, symbols, and spaces individually — and also supports katakana ⇔ hiragana conversion. Everything is processed in your browser, so your data is never sent to a server.