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Full-Width vs. Half-Width Characters: The Basics

Here are the basics of "full-width" and "half-width" characters β€” a common stumbling block in Japanese web forms.

What are full-width (zenkaku) characters

Characters with a roughly square width, including hiragana, katakana, kanji, and full-width alphanumeric characters and symbols (A, 1, etc.).

What are half-width (hankaku) characters

Characters displayed at roughly half the width of full-width characters, including half-width alphanumeric characters (A, 1), half-width katakana (ο½±ο½²ο½³), and half-width symbols.

Why the distinction is based on "width"

The concept of full-width characters arose historically from the need to display Japanese text with evenly spaced, visually clean character widths on computer screens.

Why forms often specify half-width

Fields for phone numbers, email addresses, and passwords commonly require half-width input so the system can process the data correctly.

A tip for telling them apart

At the same font size, an alphanumeric character that looks wider is full-width, and one that looks narrower is half-width. If unsure, checking your keyboard's input mode indicator (e.g., "full-width kana" or "half-width alphanumeric") is the surest way.

Half-width katakana is often avoided

Half-width katakana has a history of causing garbled text (mojibake) on certain systems, and some systems block its input entirely as a result.

Full-width and half-width are treated differently by different systems

Even the same digit "1" is treated as a different character internally by a computer depending on whether it's full-width or half-width. So even if they look similar, an error can occur if the format doesn't match what the system expects.

Switching modes in a Japanese input system

A Japanese input method (IME) lets you switch between modes like "half-width alphanumeric" and "full-width hiragana" to type the character type you need. If a form throws an error, checking your input mode first is a good first step.

Frequently Asked Questions

A form asked for half-width input, but it keeps coming out full-width β€” why?

Your Japanese input system (IME) may be turned on. Pressing the half-width/full-width key, or turning off the IME before typing again, usually resolves it.

Which should I default to using, full-width or half-width?

Japanese text itself is generally written in full-width characters, but for numbers, letters, and symbols, it's safest to follow whatever the specific system requires.