doublewidth

Doublewidth is a term used in typography and computing to describe characters that occupy two character cells in fixed-width text rendering. In monospaced environments such as terminal emulators or code editors, most ASCII characters render in a single column, while many East Asian characters—Chinese, Japanese, and Korean ideographs—render in two columns. This width distinction helps preserve legibility when mixing scripts in a single line of text.

In Unicode, the concept is captured by the East Asian Width property. Code points are classified as Wide or Fullwidth (typically occupying two columns) or as Narrow/Halfwidth (one column) and Neutral. Some systems also treat Ambiguous width code points as one or two columns depending on locale or font metrics. Width measurement is commonly provided by functions such as wcwidth and wcswidth, which return 2 for double-width code points and 1 for single-width ones; combining marks and zero-width joiners generally do not add to the total width.

Examples include Kanji, Hanzi, and other CJK characters, which are typically double-width, versus Latin letters like A, which are single-width. There are also fullwidth forms in Unicode (for example, fullwidth ASCII characters) that render as two columns, and emoji sequences that can be treated as double-width in many environments.

Applications of doublewidth awareness include proper text wrapping, alignment, and cursor positioning in terminal applications, text editors, and other software that must render multilingual text consistently. Width handling can vary by locale and font, so software often provides configurable or context-aware behavior. See also East Asian width, wcwidth, fullwidth, halfwidth.