Unicode Planes Explained: From BMP to Supplementary Characters
Unicode organises its entire code space—1,114,112 possible code points—into 17 planes. Each plane contains 65,536 code points (U+xx0000 to U+xxFFFF). Most of the characters you use every day live in Plane 0, but the other planes contain fascinating specialised content ranging from emoji to ancient scripts to private use areas. Browse all planes at the planes overview.
Plane 0: The Basic Multilingual Plane (BMP)
Plane 0, the BMP, contains essentially all modern scripts and the most commonly used symbols, punctuation, and technical characters. Latin, Greek, Cyrillic, Arabic, Hebrew, Devanagari, CJK unified ideographs, and thousands of other characters all live here. Most programming languages and text formats handle BMP characters without any special treatment—they're just a 16-bit code unit in UTF-16.
Plane 1: Supplementary Multilingual Plane (SMP)
The SMP is home to historic scripts (Linear B, Cuneiform, Egyptian Hieroglyphs), musical notation, mathematical alphanumeric symbols, and—most visibly to modern users—emoji. The Emoticons block (U+1F600–U+1F64F), Miscellaneous Symbols and Pictographs (U+1F300–U+1F5FF), and Transport and Map Symbols (U+1F680–U+1F6FF) all live here. These require UTF-16 surrogate pairs or four-byte UTF-8 sequences.
Plane 2 and 3: CJK Extension Planes
Planes 2 and 3 (and partially Plane 1) are dedicated to CJK Unified Ideograph Extensions—tens of thousands of rare and historic Han characters used in historical documents, personal names, and scholarly texts. These extensions (CJK-B through CJK-F) were added in successive Unicode versions as national standards bodies contributed characters needed for digital archiving of classical literature.
Planes 15 and 16: Private Use Areas
The entirety of Planes 15 (U+F0000–U+FFFFF) and 16 (U+100000–U+10FFFF) are designated as Supplementary Private Use Areas (SPUA-A and SPUA-B). Like the BMP's Private Use Area (U+E000–U+F8FF), these code points carry no standard meaning—organisations can assign them any character they need internally, with no risk of collision with standard Unicode assignments. Game studios, font designers, and corporate communication systems all use PUAs.