Windows-1251

On the web, it is the second most-used single-byte character encoding (or third most-used character encoding overall), and most used of the single-byte encodings supporting Cyrillic. As of January 2024^[update], 0.3% of all websites use Windows-1251. It's by far mostly used for Russian, while a small minority of Russian websites use it, with 94.6% of Russian (.ru) websites using UTF-8, and the legacy 8-bit encoding is distant second. In Linux, the encoding is known as cp1251. IBM uses code page 1251 (CCSID 1251 and euro sign extended CCSID 5347) for Windows-1251.

Windows-1251 and KOI8-R (or its Ukrainian variant KOI8-U) are much more commonly used than ISO 8859-5 (which is used by less than 0.0004% of websites). In contrast to Windows-1252 and ISO 8859-1, Windows-1251 is not closely related to ISO 8859-5.

Unicode (e.g. UTF-8) is preferred to Windows-1251 or other Cyrillic encodings in modern applications, especially on the Internet, making UTF-8 the dominant encoding for web pages. (For further discussion of Unicode's complete coverage, of 436 Cyrillic letters/code points, including for Old Cyrillic, and how single-byte character encodings, such as Windows-1251 and KOI8-R, cannot provide this, see Cyrillic script in Unicode.)

The following table shows Windows-1251. Each character is shown with its Unicode equivalent and its Alt code.

An altered version of Windows-1251 was standardised in Kazakhstan as Kazakh standard STRK1048, and is known by the label KZ-1048. It differs in the rows shown below:

Russian Amiga OS systems used a version of code page 1251 which matches Windows-1251 for the Russian subset of the Cyrillic letters, but otherwise mostly follows ISO-8859-1. This version is known as Amiga-1251, under which name it is registered with the IANA.