---
name: "utf8"
section: "5"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd", "macos"]
url: "https://new.carta.tech/utf8/5"
---

# utf8(5)

UTF-8, a transformation format of ISO 10646

## NAME

**utf8** – UTF-8, a transformation format of ISO 10646

## SYNOPSIS

**ENCODING** "UTF-8"

## DESCRIPTION

The **UTF-8** encoding represents UCS-4 characters as a sequence of octets, using between 1 and 6 for each character. It is backwards compatible with ASCII, so 0x00-0x7f refer to the ASCII character set. The multibyte encoding of non-ASCII characters consist entirely of bytes whose high order bit is set. The actual encoding is represented by the following table:

```
[0x00000000 - 0x0000007f] [00000000.0bbbbbbb] -> 0bbbbbbb
[0x00000080 - 0x000007ff] [00000bbb.bbbbbbbb] -> 110bbbbb, 10bbbbbb
[0x00000800 - 0x0000ffff] [bbbbbbbb.bbbbbbbb] ->
	1110bbbb, 10bbbbbb, 10bbbbbb
[0x00010000 - 0x001fffff] [00000000.000bbbbb.bbbbbbbb.bbbbbbbb] ->
	11110bbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
[0x00200000 - 0x03ffffff] [000000bb.bbbbbbbb.bbbbbbbb.bbbbbbbb] ->
	111110bb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
[0x04000000 - 0x7fffffff] [0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb] ->
	1111110b, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
```

If more than a single representation of a value exists (for example, 0x00; 0xC0 0x80; 0xE0 0x80 0x80) the shortest representation is always used. Longer ones are detected as an error as they pose a potential security risk, and destroy the 1:1 character:octet sequence mapping.

## SEE ALSO

[euc(5)](/euc/5.md) Rob Pike and Ken Thompson, “Hello World”, *Proceedings of the Winter 1993 USENIX Technical Conference*, USENIX Association, January 1993. F. Yergeau, *UTF-8, a transformation format of ISO 10646*, January 1998, RFC 2279. *The Unicode Standard, Version 3.0*, The Unicode Consortium, 2000, as amended by the Unicode Standard Annex #27: Unicode 3.1 and by the Unicode Standard Annex #28: Unicode 3.2.

## STANDARDS

The **utf8** encoding is compatible with RFC 2279 and Unicode 3.2.