Web Design in a Nutshell, 3rd Edition

Unicode encodings

Many character sets have only one encoding method, such as the ISO 8859 series. Unicode, however, may be encoded a number of ways. So although the code points never change, they may be represented by 1, 2, or 4 bytes. The encoding forms for Unicode are:

UTF-8

This is an expanding format that uses 1 byte for characters in the ASCII set, 2 bytes for additional character ranges, and 3 bytes for the rest of the BMP. Supplementary planes use 4 bytes. UTF-8 is the recommended Unicode encoding for web documents and other Internet technologies.

UTF-16

Uses 2 bytes for BMP characters and 4 bytes for supplementary characters. UTF-16 is another option for web documents.

UTF-32

Uses 4 bytes for all characters.

So while the code point for the percent sign is U+0025, it would be represented by the byte value 25 in UTF-8, 00 25 in UTF-16, and 00 00 00 25 by UTF-32. There are other things at work in the encoding as well, but this gives you a feel for the difference in encoding forms.