ASCII Table

The ASCII table lists the 128 characters of the American Standard Code for Information Interchange, the 1963 standard that still underpins how computers exchange text. Each character gets a number from 0 to 127, shown here in decimal, hexadecimal and binary, so the same table serves programmers reading hex dumps and students decoding binary homework.

The table splits into three zones. Codes 0 to 31 are control characters: invisible instructions like Line Feed (10), Carriage Return (13) or Escape (27) that once drove teletypes and still shape file formats today, since every line break in a text file is one of these bytes. Codes 32 to 126 are the printable characters: the space (32), punctuation, digits, and both alphabets. Code 127 (DEL) closes the set, a leftover from paper tape where punching all seven holes erased a character.

A few anchor codes make the whole table easy to navigate. Uppercase A is 65 and the alphabet runs in order from there, so Z is 90. Lowercase a is 97, exactly 32 above its uppercase twin, which means switching case flips a single bit. The digit 0 is code 48, not 0, a distinction that explains a classic programming bug: the character 7 has code 55, and forgetting to subtract 48 turns arithmetic into nonsense.

ASCII only covers 7 bits, and that limitation is precisely why it survived. UTF-8, the encoding used by the vast majority of the web, was designed so that codes 0 to 127 are encoded as the same single bytes as ASCII. Every ASCII file is already valid UTF-8, and any byte below 128 in a UTF-8 stream means exactly what this table says. Accented letters, symbols and emoji live above this range, built from multi-byte sequences that never collide with these 128 codes.