Full-width / Half-width Converter
Convert between full-width and half-width for alphanumerics, symbols, spaces, and katakana. Voiced and semi-voiced marks handled correctly.
About this tool
"Full-width" and "half-width" refer to character width. Full-width characters are as wide as Japanese (Ａ, １, カ); half-width are half as wide (A, 1, ｶ). The same "A" full-width and half-width are treated as different characters by computers, so a mix of them can break matching and search. This tool converts between full-width and half-width in your browser and never sends your input anywhere.
When do you need it?
- Normalizing form input — full-width digits in a phone or postal number may be rejected; unify to half-width.
- Cleaning data — mixed full/half-width digits and letters in CSV or spreadsheets break aggregation and matching.
- Consistent appearance — making alphanumerics half-width within Japanese text improves readability.
What gets converted
Generally, alphanumerics, symbols, spaces, and katakana exist in both widths; hiragana and kanji have no half-width form. Half-width katakana (ｶﾀｶﾅ) appears mainly in legacy systems and forms, but can cause mojibake in some environments, so it is often unified to full-width depending on the use.
Watch combining voiced marks
In half-width katakana, the voiced/semi-voiced marks are separate characters (e.g. ｶ + ﾞ = ガ). Converting to full-width makes it look like a single "ガ," but internally it requires combining. This can cause discrepancies in character counting or string processing, so take care with data containing half-width kana.
A rule of thumb
For normalizing input data and system integration, use half-width; for Japanese prose meant to be read, use full and half-width appropriately for readability. Batch-convert to fit the use case.
How to use
- Enter text and choose which classes to convert (alphanumerics, symbols, space, katakana).
- Press "To half-width" or "To full-width" to see the result and copy it.
FAQ
Are the characters I enter sent to a server?
No. All conversion runs in your browser, so the characters you enter never leave your device.
What is the difference between full-width and half-width?
Beyond the visual width, they are handled internally as different character codes. So "Ａ" and "A" are distinct characters to a computer, which can cause mismatches in search and comparison.
Are half-width voiced kana (ガ, パ, etc.) converted correctly?
Yes. In half-width kana, voiced and semi-voiced sounds are written as two characters (like カ + ゛), and this tool correctly combines them into a single character such as ガ when converting to full-width — and splits them back in the reverse direction.
Can I convert only alphanumerics, or only katakana?
Yes. You can select which targets (alphanumerics, symbols, spaces, katakana) to convert, so you normalize only the types you need.
Are hiragana and kanji converted too?
No. Hiragana and kanji have no full-width/half-width distinction, so they are out of scope. The tool converts alphanumerics, symbols, spaces, and katakana.
When is this useful?
For unifying notation before form registration, resolving inconsistencies in CSV or ledger data, and reformatting text to a system's required format. Consistent notation reduces input errors and matching mistakes.