How to Fix Full-width and Half-width Errors on Japanese Websites
Japanese websites may strictly distinguish between different character types when processing account registration or address information. One common example is the distinction between full-width and half-width characters. Refer to the guide below and convert your text to the required format.
Common full-width / half-width requirements by field type
| Field | Typical requirement | Correct example |
|---|---|---|
| Name furigana (katakana) | Full-width katakana is usually required | ヤマダ |
| Postal code / Phone number | Half-width digits are usually required; check whether hyphens are allowed | 1234567 / 01012345678 |
| Street number / Apartment number | Varies by site; try switching if you get an error | 1-2-3 or １－２－３ |
| Email address / Password | Half-width letters, digits, and symbols are usually required | [email protected] |
Why full-width errors occur on Japanese shopping sites
Characters that look nearly identical — the Latin letter A vs. Ａ,
the digit 1 vs. １, or the katakana ｶ vs. カ —
are treated as completely different codes by the underlying system.
Full-width and half-width characters can easily get mixed in when you paste an address from another app,
copy text from a website, or rely on smartphone autocomplete.
Furigana input: full-width vs. half-width katakana
Furigana (phonetic reading) fields on Japanese websites typically require full-width katakana. If you entered your name in katakana but keep getting an error, the problem may be that half-width katakana was used instead. Use the [Half-width katakana → Full-width katakana] option on this page to fix it.
*Note: Some older reservation or shipping systems specifically require half-width katakana (半角カナ). Always check the exact wording of the error message.
Full-width digits vs. half-width digits
Full-width digits like １２３４ take up a square cell each,
while half-width digits 1234 use standard ASCII width.
Payment card numbers, postal codes, and phone number fields often reject full-width digits.
Use [Full-width ASCII → Half-width ASCII] to normalize them.
The invisible full-width space problem
One of the trickiest error sources is the space character.
When a Japanese IME is active or [Alt + =] is toggled in Windows, pressing the spacebar can insert a full-width space ( )
instead of a regular half-width space.
A full-width space hidden between a first and last name, inside an address,
or before a building name can cause a form to reject the input entirely.
If you cannot find the cause of an error,
try running [Full-width space → Half-width space].
Bulk text cleanup with NFKC normalization
When collecting Japanese product names at scale for data analysis,
or preparing listings for an online store, NFKC normalization is a handy one-step cleanup.
It converts compatibility characters like ①, Ⅳ,
and ㍿ alongside full-width alphanumerics into standard text
(1, IV, 株式会社), making search and comparison far more reliable.
Checklist when you hit an error on a Japanese site
- Are phone numbers, postal codes, and card numbers in half-width digits?
(e.g.
1234) - Is the furigana field filled with full-width katakana?
(e.g.
ヤマダ) - Is there an invisible full-width space hiding somewhere in the text?
- Do any compatibility characters (
①,Ⅰ, etc.) appear in addresses or product names?