Halfwidth

Halfwidth is a term used in typography and computing to describe characters that occupy half the width of a typical full-width character cell, a concept particularly relevant in East Asian text layouts. In many fixed-width or monospaced fonts, Latin letters and some Katakana are rendered as halfwidth, meaning they fit into a single character cell, while many CJK ideographs are fullwidth and occupy two cells.

Unicode maintains a Halfwidth and Fullwidth Forms block (U+FF00 to U+FFEF) that includes both halfwidth characters and their fullwidth counterparts. The most common example is halfwidth Katakana, found in the range U+FF61 to U+FF9F, such as the character ｶ (U+FF76) and the diacritic marks ﾞ (U+FF9E) and ﾟ (U+FF9F). These characters are used primarily for compatibility with legacy encodings and input methods that require limited display width.

In practice, halfwidth is used to save display space or preserve alignment in environments where a fixed column width is important, such as certain terminal emulators, legacy Japanese encodings (including Shift JIS and EUC-JP), and some text editors. By contrast, fullwidth characters are designed to occupy the same visual space as CJK ideographs, aiding alignment in mixed-language text.

Notes on width can depend on font, rendering engine, and the East Asian Width classification in Unicode. Consequently, the perceived width of halfwidth versus fullwidth characters may vary across platforms and contexts.