East Asian Width

What is East Asian Width?

East Asian Width is a Unicode character property defined in UAX #11 — East Asian Width that classifies characters according to the display width they should occupy in fixed-width (monospaced) rendering environments, particularly traditional East Asian terminals and text layouts. The property answers the question: "Does this character occupy one column or two columns when displayed in a terminal or monospaced layout?"

The property was introduced because East Asian scripts — Chinese, Japanese, Korean — were historically displayed at twice the width of ASCII characters on fixed-pitch terminals. Mixing ASCII and CJK text in a single terminal line required a consistent model for how much horizontal space each character would consume.

The Six Width Categories

Terminal Implications

In a terminal emulator, the renderer must know the East Asian Width of every character to correctly advance the cursor. If a Wide or Fullwidth character is assumed to be narrow, subsequent characters will overwrite existing content, causing display corruption.

The POSIX standard function wcwidth() (from <wchar.h>) returns 0 for combining characters, 1 for narrow characters, and 2 for wide characters. Modern terminal emulators implement wcwidth() based on UAX #11 data.

# Python: get East Asian Width property
import unicodedata

def display_width(char: str) -> int:
    # Return terminal display width of a single character.
    eaw = unicodedata.east_asian_width(char)
    return 2 if eaw in ("W", "F") else 1

# Examples
display_width("A")   # → 1 (Narrow)
display_width("漢")  # → 2 (Wide)
display_width("Ａ")  # → 2 (Fullwidth)
display_width("ｱ")  # → 1 (Halfwidth)

The wcwidth Python package provides a conformant implementation updated with each Unicode release.

The Ambiguous Category

Characters with Ambiguous (A) width are the most problematic in practice. Their width is context-dependent:

• In an East Asian context (a terminal set to a CJK locale), they display as Wide (2 columns)
• In a Western context, they display as Narrow (1 column)

This affects many common symbols: degree sign (°), copyright symbol (©), Greek letters (α, β), and many box-drawing characters. Terminal emulators that serve mixed-locale user bases must make a policy choice, and mismatches between the application and terminal settings cause visible misalignment.

Quick Facts