CJK Unified Ideographs: The Largest Unicode Block
The CJK Unified Ideographs block (U+4E00–U+9FFF) is the largest single block in the Unicode Basic Multilingual Plane, containing 20,902 Han characters used in Chinese, Japanese, and Korean writing. Combined with its extensions spread across the BMP and supplementary planes, CJK coverage in Unicode exceeds 90,000 characters—making Han script the most extensively encoded writing system in Unicode.
What "Unified" Means
Before Unicode, China, Japan, and Korea each had their own national character standards (GB2312, JIS X 0208, KS X 1001). Many Han characters appear in all three standards but with slightly different glyphs. Rather than encoding each national variant separately, the Unicode CJK Unified Ideographs committee (Ideographic Research Group) unified characters with the same abstract semantics into a single code point. The specific glyph variant is left to the font—a Chinese, Japanese, and Korean font may render U+8FBA differently, in keeping with each country's typographic conventions.
The Extension Blocks
The original CJK block filled quickly with the most commonly used characters. Subsequent Unicode versions added:
- CJK Extension A (U+3400–U+4DBF): 6,592 rare and historic characters. Added in Unicode 3.0.
- CJK Extension B (U+20000–U+2A6DF): 42,711 characters in Plane 2. Added in Unicode 3.1.
- CJK Extension C through G: Further extensions in Planes 2 and 3, added through Unicode 13.
- CJK Extension H (U+31350–U+323AF): Added in Unicode 15.0.
Many characters in Extensions B and above are needed for historical documents, classical poetry, and personal names (a significant practical issue—many East Asian people have names containing rare characters not in the original block).
Sorting CJK Characters
Sorting Han characters is complex. Options include: by pronunciation (pinyin in Mandarin, readings in Japanese), by radical and stroke count (the traditional dictionary order), or by frequency of use. There is no single correct order—applications serving Chinese, Japanese, and Korean users typically need to support multiple collation methods. Use the scripts browser to explore the Han script and its blocks.