Windows-1252

What is Windows-1252?

Windows-1252 (also known as CP1252 or the "ANSI" code page) is an 8-bit character encoding developed by Microsoft as an extension of ISO 8859-1 (Latin-1). It adds 27 printable characters in the range 0x80–0x9F — the region that ISO 8859-1 reserves for C1 control characters — making it more useful in practice for Western European typography.

Windows-1252 became one of the most widely deployed encodings in history because it was the default code page for English and Western European editions of Windows from Windows 3.1 through Windows XP. Any text file created on a Western European Windows system and not explicitly encoded as UTF-8 is almost certainly Windows-1252.

How Windows-1252 Differs from Latin-1

ISO 8859-1 leaves the range 0x80–0x9F defined as non-printable C1 control characters. Windows-1252 repurposes this range for useful typographic characters:

The range 0xA0–0xFF is identical between Windows-1252 and ISO 8859-1.

The Browser Compatibility Problem

For over a decade, web browsers diverged from the HTTP standard on encoding. HTTP/1.1 specified that text/html; charset=ISO-8859-1 meant pure ISO 8859-1. But because so many real-world pages were served with this declaration while actually containing Windows-1252 bytes (smart quotes, em dashes, Euro signs), browsers silently treated ISO-8859-1 as Windows-1252.

This was eventually formalized: the WHATWG Encoding Standard (used by all modern browsers) defines ISO-8859-1 as an alias for windows-1252. If a page declares charset=ISO-8859-1, browsers now treat it as Windows-1252.

Code Examples

# Windows-1252 in Python
text = 'Hello \u2013 world'  # En dash
encoded = text.encode('windows-1252')
print(encoded)  # b'Hello \x96 world'

# Smart quotes
smart = '\u201cHello\u201d'  # "Hello"
encoded = smart.encode('windows-1252')
print(encoded)  # b'\x93Hello\x94'

# What Latin-1 sees for those bytes
b'\x93Hello\x94'.decode('latin-1')   # '\x93Hello\x94' — C1 controls, not quotes
b'\x93Hello\x94'.decode('cp1252')    # '"Hello"' — correct

# Detecting the classic mojibake pattern
# UTF-8 é (0xC3 0xA9) read as CP1252 → 'é'
b'\xc3\xa9'.decode('cp1252')  # 'é'

// Node.js: explicit Windows-1252 decoding
const iconv = require('iconv-lite');
const buf = Buffer.from([0x93, 0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x94]);
iconv.decode(buf, 'win1252');  // '"Hello"'

Quick Facts

Common Pitfalls

The "ANSI" misnomer. Windows users and older Microsoft documentation call Windows-1252 "ANSI," but ANSI (the American National Standards Institute) never defined this encoding. The term persists in Windows API functions like CreateFileA (ANSI) vs. CreateFileW (Wide/Unicode), referring to the system code page, which is often but not always CP1252.

Smart quotes and mojibake. Microsoft Word documents saved as plain text often contain Windows-1252 smart quotes (0x91–0x94) and em/en dashes (0x96–0x97). When these files are treated as ISO 8859-1 or UTF-8, these characters appear as garbled symbols. The ftfy Python library can automatically fix many of these mojibake patterns.

The Euro sign hazard. The Euro sign (€) is at 0x80 in Windows-1252 but at U+20AC in Unicode (encoded as 3 bytes E2 82 AC in UTF-8). A CP1252 file with a Euro sign, incorrectly parsed as UTF-8, will throw a UnicodeDecodeError or produce garbage characters.