ASCII Table

How to use the ASCII table and converter

Type or paste text in the Text box to get its codes, or type codes in the Codes box to turn them back into text — each box updates the other. Pick decimal, hex, binary or octal and the codes are rewritten in that base. The working below the boxes breaks every character into its binary place values. Unseparated byte strings such as 48656C6C6F or 0100100001101001 are split into bytes automatically.

The table lists all 128 ASCII characters. Filter it by typing a character, a code in any base, an abbreviation such as ESC, a word such as bracket, or an entity such as <, or use the buttons to show only control characters, letters, digits or symbols.

How to read the codes

Each character has one number. The decimal, hexadecimal, octal and binary columns are the same number written in base 10, 16, 8 and 2. In binary, every position is a power of two, so:

code = b₆×64 + b₅×32 + b₄×16 + b₃×8 + b₂×4 + b₁×2 + b₀×1

One hex digit stands for exactly four bits and one octal digit for three, which is why programmers prefer hex: 0100 0001 is 4 and 1, so A is hex 41.

Worked example: “Hi!”

This is the example the converter shows before you type anything:

• H = 72 = 64 + 8 → binary 01001000, hex 48, octal 110
• i = 105 = 64 + 32 + 8 + 1 → binary 01101001, hex 69, octal 151
• ! = 33 = 32 + 1 → binary 00100001, hex 21, octal 041

So “Hi!” is 72 105 33 in decimal and 48 69 21 in hex — three characters, three bytes. To practice the conversions by hand, try the binary to decimal and hex to decimal converters.

Control characters and printable characters

Codes 0–31 and 127 are the 33 control characters. They were designed to drive teleprinters and data links — ring a bell, return the carriage, mark the end of a transmission — rather than to be printed. A few are still everywhere: tab (9), line feed (10), carriage return (13), escape (27, which starts terminal color codes) and NUL (0, the end of a C string). DEL (127) is all seven bits set to 1, so on punched paper tape it could overwrite any mistake.

Codes 32–126 are the 95 printable characters: the space, the digits, the 26 capital and 26 small letters, and 32 punctuation marks and symbols. The layout is deliberate. Digits start at 48 (hex 30), so a digit’s value is its code minus 48. Capital letters start at 65 and small letters at 97, exactly 32 apart: changing case flips a single bit (bit 5), which is how simple case conversion works for English text.

A short history of ASCII

ASCII — the American Standard Code for Information Interchange — was first published in 1963 as ASA X3.4-1963 by the American Standards Association, the body that later became ANSI. It is a 7-bit code, giving 128 values. The 1963 edition had no small letters; they were added in the 1967 revision, and the standard was last revised as ANSI X3.4-1986. The same repertoire was adopted internationally as ISO/IEC 646.

In 1969, RFC 20 by Vint Cerf proposed ASCII for the ARPANET, the Internet’s predecessor, using “7-bit ASCII embedded in an 8 bit byte whose high order bit is always 0” — which is why the binary column above always starts with 0. RFC 20 is now Internet Standard STD 80, and protocols such as HTTP still define their syntax in terms of ASCII.

ASCII, Unicode and UTF-8

Unicode kept ASCII as its first block: code points U+0000 to U+007F are exactly the 128 ASCII characters in the same order. UTF-8, the encoding used by almost every web page, writes those code points as one byte each with the same value, and writes every other character as two to four bytes that are all 128 or higher. So plain ASCII text is already valid UTF-8, and a byte below 128 in UTF-8 always means the ASCII character in this table.

Anything else is not ASCII. The converter shows such characters as Unicode code points and lists their UTF-8 bytes — for example, é is U+00E9, stored as the two bytes C3 A9. If those bytes are wrongly read as Windows-1252 they appear as “é”, the familiar garbled-text problem. Other common non-ASCII look-alikes are curly quotes (’ is U+2019), the en dash (– is U+2013) and the no-break space (U+00A0,  ).

Common mistakes

• The digit 0 is not NUL. The character “0” is code 48; code 0 is the invisible NUL control character.
• Line endings differ. LF on Linux and macOS, CR LF on Windows — convert when a file’s lines look joined or show ^M.
• “ASCII” files with é or € in them are really UTF-8 or a legacy code page; ASCII stops at 127.
• Escaping HTML: only & and < must be escaped in text (and quotes inside attribute values); everything else can be typed as-is in a UTF-8 page.

More web references: HTML color codes and HTTP status codes, or count characters with the word counter.