Fullwidth Digit Two

It still means two; the wider form marks text width.

The fullwidth 2 has the same numeric value as ordinary 2; Unicode gives it a compatibility mapping to 2. In fixed-width East Asian text, its design reserves the space of a fullwidth character, helping numbers line up with nearby text. “Fullwidth” describes a text convention, not a fixed measurement: a proportional font may not render a fullwidth 2 as exactly twice the width of 2.

What were fullwidth forms made for?

To fit East Asian layouts that mixed wide and narrow characters. Fullwidth forms grew out of mixed-width computing: ideographs occupied a full character cell, while Western letters and digits were narrower. A fullwidth digit let numbers line up with surrounding text. Zenkaku (“fullwidth”) and hankaku (“halfwidth”) are Japanese terms for these styles; the width distinction also serves Chinese and Korean text.

JIS C 6226-1978, a Japanese character-encoding standard, was established in January 1978; Japan's first Japanese-language word processor followed that year. Unicode retained paired fullwidth forms so older mixed-width text could be converted and back again.

When should you use ２ instead of 2?

Use it only when a field or layout asks for fullwidth.

Use the zenkaku digit 2 when a field requests the wide form. Some Japanese government forms treat fullwidth and halfwidth digits as separate input classes; postal-code guidance also shows fields that require halfwidth digits, where ２ may be rejected. If no width is specified, ordinary 2 is the safer entry for numeric fields.