Unicode Planes

The Unicode codespace is the full range of possible code points that can be assigned to characters, spanning from U+0000 to U+10FFFF. To organize this large space, Unicode divides it into 17 planes, numbered from 0 to 16. Each plane contains exactly 65,536 code points (that is, 0x0000–0xFFFF within that plane), giving a total capacity of just over one million possible characters. This structured layout helps group related characters together and makes it easier to manage the continual expansion of the standard as new scripts, symbols, and use cases are added.

Plane 0 is known as the Basic Multilingual Plane (BMP), covering U+0000 to U+FFFF. It includes the vast majority of characters used in everyday text: Latin, Greek, and Cyrillic alphabets; common punctuation; digits; and many widely used symbols. It also contains large portions of scripts such as Arabic, Hebrew, Devanagari, and others, along with the core set of CJK (Chinese, Japanese, Korean) ideographs. Because of this, many older systems and programming environments were originally designed around the BMP alone, which is why characters outside this plane are sometimes referred to as “supplementary characters.”

The remaining 16 planes (Planes 1–16) are called the supplementary planes and hold a wide variety of additional content. For example, Plane 1 (the Supplementary Multilingual Plane) includes historic scripts, musical notation, and many emoji; Plane 2 (the Supplementary Ideographic Plane) contains extended sets of CJK ideographs; and other planes are dedicated to specialized uses such as additional ideographic extensions, symbols, and large private-use areas where developers can define their own characters. Together, these planes ensure that Unicode can accommodate both modern and ancient writing systems, as well as the growing demand for symbols and pictographic characters across digital platforms.