Last updated: March 2026
What is ASCII?
ASCII is the foundational character encoding standard that has been used since 1963. It assigns a unique number (0-127) to each character, including letters, digits, punctuation, and control codes. When you press 'A' on your keyboard, the computer stores the number 65.
While Unicode and UTF-8 have largely replaced ASCII for international text, ASCII remains the core — the first 128 characters in UTF-8 are identical to ASCII. Understanding ASCII is fundamental to computer science and programming.
Printable vs Control Characters
Printable characters (32-126) are the ones you can see — letters, numbers, symbols, and the space character. There are 95 of them. They're the characters you'll encounter most often in programming and text processing.
Control characters (0-31, 127) are invisible and were originally designed to control hardware like printers and terminals. The most commonly used today are TAB (9), LF/Line Feed (10) for Unix newlines, and CR (13) for Windows newlines (CRLF = 13+10).
Frequently Asked Questions
What is ASCII?
ASCII (American Standard Code for Information Interchange) is a character encoding standard from 1963 that assigns numbers 0-127 to characters. It includes 33 control characters (0-31, 127), a space (32), and 94 printable characters (33-126) including letters, digits, and symbols.
What are ASCII control characters?
Characters 0-31 and 127 are control characters — non-printable codes used for device control. Common ones: NULL (0), TAB (9), LF/Line Feed (10), CR/Carriage Return (13), ESC (27). Most originated for teletype machines and serial communications.
How many characters are in ASCII?
ASCII defines 128 characters (0-127), using 7 bits. Of these, 95 are printable (space through tilde ~) and 33 are control characters. Extended ASCII (128-255) varies by system and adds accented letters and symbols.
What is the ASCII value of A?
Uppercase 'A' is ASCII 65 (hex 41, binary 01000001). Lowercase 'a' is 97 (hex 61, binary 01100001). The difference between uppercase and lowercase is always 32 — a convenient feature that makes case conversion simple in code.
What replaced ASCII?
Unicode (and its encoding UTF-8) is the modern successor to ASCII. UTF-8 is backward-compatible — the first 128 characters are identical to ASCII. But UTF-8 extends to over 1.1 million characters, covering every writing system and emoji. Over 98% of websites use UTF-8.
Why does ASCII start at 0?
Character 0 (NULL) was originally used as a 'do nothing' filler in paper tape. Characters 1-31 are control codes for equipment. Printable characters start at 32 (space). Digits 0-9 start at 48, uppercase letters at 65, lowercase at 97. This ordering was designed to simplify sorting and comparison.