ASCII Table

What is ASCII?

ASCII (American Standard Code for Information Interchange) is a 7-bit character encoding standard published in 1963. It maps 128 characters — English letters, digits, punctuation, and control codes — to numeric values 0 through 127. Its code-point assignments remain widely reused; UTF-8 preserves all 128 as the same single-byte values.

ASCII vs Unicode

ASCII covers 128 characters — sufficient for basic English text. Unicode 17.0 assigns 159,801 graphic and format characters across 172 scripts, including CJK characters, emoji, mathematical symbols, and historical scripts. UTF-8, the dominant Unicode encoding, is backward-compatible with ASCII: bytes 0–127 map to the same characters in both. This is why ASCII knowledge remains relevant — it is the common subset shared by the two encodings.

Control Characters in Current Systems

Most ASCII control codes came from teleprinters, but several still affect files, terminals, and protocols. NUL (00) terminates strings in C. HT (09) is a tab, while LF (0A) and CR (0D) form common line endings. Terminal escape sequences begin with ESC (1B).

Hidden controls can change parsing even when the text looks normal. Inspect the byte values when a CSV row splits in the wrong place, a shell prompt changes color unexpectedly, or a Windows text file shows extra line breaks on another system.

Extended ASCII Is Not One Table

Standard ASCII stops at 127. The name "extended ASCII" refers to several incompatible 8-bit encodings, including ISO-8859-1, Windows-1252, and IBM code page 437. They agree on codes 0–127 but assign different characters to some values from 128 through 255. A byte such as E9 therefore needs an encoding label before it can be interpreted correctly.

Use UTF-8 for new text formats unless a protocol specifies another encoding. The ASCII, UTF-8, and Unicode guide explains the distinction between character sets, code points, and byte encodings.

Look Up ASCII Values in Code

The same 0–127 mapping is available through standard language functions:

// JavaScript
'A'.charCodeAt(0);       // 65
String.fromCharCode(65); // "A"

# Python
ord('A')  # 65
chr(65)   # 'A'

// Java
(int) 'A';  // 65
(char) 65;  // 'A'

Checking Whether Text Is Pure ASCII

Validate the complete string before treating character positions as one-byte ASCII values:

// JavaScript
function isAscii(text) {
  return /^[\x00-\x7F]*$/.test(text);
}

isAscii('Hello World'); // true
isAscii('Café');        // false

# Python 3.7+
'Hello World'.isascii()  # True
'Café'.isascii()         # False

Check that every code point is at most 127 before labeling text as ASCII. For whole strings, the ASCII code converter handles one-character lookups, while the text to hex converter encodes complete text input.

For strict byte-pair parsing and complete implementations in Python, JavaScript, C, and shell, use the hex to ASCII programming guide and its ASCII to hex companion.

Inspecting Printable ASCII in Binary Data

Filtering bytes from 32 through 126 is a quick way to extract possible ASCII strings from a file. It is deliberately lossy: it removes offsets, controls, and every non-ASCII byte, so it must not be used to reconstruct the original data.

# Python: extract only printable ASCII bytes
with open('data.bin', 'rb') as file:
    data = file.read()
    printable = ''.join(chr(byte) for byte in data if 32 <= byte <= 126)
    print(printable)

Use the hex decoder when offsets, control bytes, UTF-8 validity, or file signatures matter; it can inspect a local file without uploading it.

Base64 Uses an ASCII Alphabet

Standard Base64 represents binary data with the ASCII characters A–Z, a–z, 0–9, +, and /, plus optional = padding. Every complete group of 3 input bytes (24 bits) becomes 4 Base64 characters (6 bits each), making the encoded form about 33% larger before padding. Base64 is an encoding, not encryption or integrity protection.

// Browser example for an ASCII-only string
btoa('Hello');      // 'SGVsbG8='
atob('SGVsbG8=');   // 'Hello'

Browser btoa() accepts a binary string whose code units fit in one byte; encode arbitrary Unicode text to bytes first. RFC 4648 defines standard Base64 and the separate base64url alphabet used by URL-safe formats.

Primary References

• RFC 20: ASCII Format for Network Interchange
• The Unicode Standard, Version 17.0
• Unicode 17.0 Character Counts
• RFC 3629: UTF-8
• RFC 4648: Base16, Base64, and Base64url

Related Tools

Use our ASCII Code Converter to look up individual characters and convert between decimal, hex, binary, and octal formats. To convert entire strings, try the Hex to ASCII converter or the Text to Hex converter.