What Does 全角 Mean?

1. Compare full-width and half-width characters

Width is part of the character data, not merely a font setting. Similar-looking text can therefore fail an exact validation rule.

2. Translate the instruction beside the field

• 全角で入力してください: enter using full-width characters.
• 全角カタカナで入力してください: enter using full-width Katakana.
• 全角英数字: full-width Latin letters and numbers.
• 半角英数字: half-width Latin letters and numbers.
• 半角数字: half-width numbers, usually 0–9 from a standard keyboard.

3. Check spaces, punctuation, and Katakana

Changing ABC to ＡＢＣ may not be enough. A copied value can also contain a normal space, a full-width Japanese space, a half-width hyphen, or half-width Katakana. Convert the whole field, then compare it with the form’s example.

Standard Japanese Katakana such as テスト is already full-width. Half-width Katakana such as ﾃｽﾄ uses a smaller legacy character set, so voiced marks can also be represented separately.

4. Fix a width error in a safe order

1. Copy only the value from the rejected field.
2. Identify whether the message says 全角, 半角, カタカナ, 英字, or 数字.
3. Convert only the character types requested.
4. Remove unsupported spaces or punctuation only if the form says to do so.
5. Paste the result back and check that browser autofill did not restore the old value.

5. Avoid common width mistakes

• Converting letters but leaving the wrong kind of space.
• Using ﾃｽﾄ when the form asks for full-width カタカナ.
• Assuming 全角 is a visual font setting or always means Japanese-only text.
• Equating full-width with a fixed byte length.
• Copying punctuation from another app without checking its width.

6. Use the form’s example as the final rule

Japanese form validators can apply field-specific rules that go beyond character width: permitted punctuation, a required kana reading, a maximum number of characters, or a half-width postal code. Convert only the rejected value, keep a copy of the original, and do not change a legal name or address merely to satisfy a display preference.

If a form still rejects a correctly converted value, read the full message and check the field label. The Japanese Form Helper can explain common instructions, while the site owner’s help channel is the right source for account-specific requirements.