Unicode Transformation Formats

UTF-8 is a character encoding standard used for electronic communication. Defined by the Unicode Standard, the name is derived from Unicode Transformation Format 8-bit. As of 2026, almost every webpage (99%) is transmitted as UTF-8.

UTF-16 (16-bit Unicode Transformation Format) is a character encoding that supports all 1,112,064 valid code points of Unicode. The encoding is variable-length as code points are encoded with one or two code units. UTF-16 arose from an earlier obsolete fixed-width 16-bit encoding now known as UCS-2 (for 2-byte Universal Character Set), once it became clear that more than 216 (65,536) code points were needed, including most emoji and important CJK characters such as for personal and place names.

Punycode is a representation of Unicode with the limited ASCII character subset used for Internet hostnames. Using Punycode, host names containing Unicode characters are transcoded to a subset of ASCII consisting of letters, digits, and hyphens, which is called the letter–digit–hyphen (LDH) subset. For example, the German München (English: Munich) is encoded as Mnchen-3ya.

UTF-32 (32-bit Unicode Transformation Format), sometimes called UCS-4, is a fixed-length encoding used to encode Unicode code points that uses exactly 32 bits (four bytes) per code point (but a number of leading bits must be zero as there are far fewer than 232 Unicode code points, needing actually only 21 bits). In contrast, all other Unicode transformation formats are variable-length encodings. Each 32-bit value in UTF-32 represents one Unicode code point and is exactly equal to that code point's numerical value.

UTF-7 (7-bit Unicode Transformation Format) is an obsolete variable-length character encoding for representing Unicode text using a stream of ASCII characters. It was originally intended to provide a means of encoding Unicode text for use in Internet E-mail messages that was more efficient than the combination of UTF-8 with quoted-printable.

character encoding standardized in P.R. of China and mostly used for Simplified Chinese, compatible with the universal character set defined in The Unicode® Standard and the ISO/IEC 10646 standard, backward compatible with GB encodings

Unicode Technical Standard for reducing the number of bytes needed to represent Unicode text

UTF-EBCDIC is a character encoding capable of encoding all 1,112,064 valid character code points in Unicode using 1 to 5 bytes (in contrast to a maximum of 4 for UTF-8). It is meant to be EBCDIC-friendly, so that legacy EBCDIC applications on mainframes may process the characters without much difficulty. Its advantages for existing EBCDIC-based systems are similar to UTF-8's advantages for existing ASCII-based systems. Details on UTF-EBCDIC are defined in Unicode Technical Report #16.

The Compatibility Encoding Scheme for UTF-16: 8-Bit (CESU-8) is a variant of UTF-8 that is described in Unicode Technical Report #26. A Unicode code point from the Basic Multilingual Plane (BMP), i.e. a code point in the range to , is encoded in the same way as in UTF-8. A Unicode supplementary character, i.e. a code point in the range to , is first represented as a surrogate pair, like in UTF-16, and then each surrogate code point is encoded in UTF-8. Therefore, CESU-8 needs six bytes (3 bytes per surrogate) for each Unicode supplementary character while UTF-8 needs only four. Though not spec

UTF-1 is an obsolete method of transforming ISO/IEC 10646/Unicode into a stream of bytes. Its design does not provide self-synchronization, which makes searching for substrings and error recovery difficult. It reuses the ASCII printing characters for multi-byte encodings, making it unsuited for some uses (for instance Unix filenames cannot contain the byte value used for forward slash). UTF-1 is also slow to encode or decode due to its use of division and multiplication by a number which is not a power of 2. Due to these issues, it did not gain acceptance and was quickly replaced by UTF-8.

MIME compatible Unicode compression scheme