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ASCII Character lookup table

A complete ASCII character query comparison tool. Covers all codes from 0-255, supports real-time search of Decimal, Hex, Binary, and Unicode, and has built-in text converter, favorites, and recent query functions.

ASCII converter Supports Decimal / Hex / Binary / Octal conversion
Input format:
After entering the content, click Convert...
Output format:
Commonly used control characters
ASCII character table 128 pen

What is ASCII?

ASCII (American Standard Code for Information Interchange, American Standard Code for Information Interchange) is the most basic character encoding standard in computer systems. It uses 7 bits to represent 128 characters, including English letters (A-Z, a-z), numbers (0-9), punctuation marks and control characters.

The ASCII encoding was first released in 1963 and was originally designed for telegraph communications. Because of its simplicity and universality, it is still the basis for all modern text encoding systems (such as Unicode, UTF-8).

Key points: ASCII only uses 7 bits (0–127) because early communication lines could only transmit 7 bits of data at a time, and the 8th bit was usually used for parity.

Differences between ASCII and Unicode

Compare items ASCII Unicode
number of bits7 bitsVariable (UTF-8, UTF-16, UTF-32)
Number of characters128 (basic)More than 149,000
Language supportEnglish onlyAll languages around the world + emojis
Compatibility—Forward compatible ASCII (UTF-8)
Release year19631991
Application scenariosOld system, embedded, pure EnglishWeb, modern apps, multilingual

LF, CR, CRLF difference

All three are "line feed" symbols, but different operating systems use different conventions:

symbol numerical value Use the system Description
LF10 (0x0A)Linux / macOSLine Feed, the cursor moves down one line
CR13 (0x0D)Classic Mac (OS 9)Carriage Return, the cursor returns to the beginning of the line
CRLF13 10 (0x0D 0x0A)WindowsCarriage return + line feed, combination of the two

Git can be found in .gitattributes Set the automatic conversion of line breaks between different platforms.

Why does ASCII only have 128 characters?

ASCII uses a 7-bit encoding, 2⁷ = 128, so it can only represent up to 128 characters. Here’s why:

  • Historical restrictions: Communications equipment in the 1960s used 7-bit transmission, with the 8th bit reserved as a parity bit for basic error detection.
  • Cost considerations: At that time, memory and storage space were extremely expensive, and 7 bits was enough to cover all English letters, numbers, and basic symbols.
  • Design goals: ASCII is designed for English only and does not need to accommodate characters from other languages.

Later, in order to solve the problem of insufficient 128 characters, Extended ASCII (Extended ASCII, 128–255) and the final Unicode standard appeared.

ASCII FAQ

What is Extended ASCII?
Extended ASCII is an encoding that extends standard ASCII (0–127) to 8 bits (128–255). However, because there is no unified standard, different systems (such as IBM PC, Apple Mac) use different Code Pages, resulting in the same value of 128–255 may display different characters on different systems. Common Code Pages include Windows-1252, ISO-8859-1 (Latin-1), etc.
What is the relationship between ASCII and UTF-8?
UTF-8 is an encoding of Unicode that is fully backwards compatible with ASCII. That is, all ASCII characters (0–127) are encoded exactly the same as ASCII in UTF-8 (requiring only 1 byte). Therefore, any valid ASCII text is also a valid UTF-8 text. This is why UTF-8 has become the most mainstream encoding method on the Internet.
How to query the ASCII value of a character?
Several methods can be used:
1. Programming language:'A'.charCodeAt(0)(JavaScript) or ord('A')（Python）
2. Enter text directly in the "ASCII Converter" of this tool to see the corresponding decimal value.
3. Enter characters in the search box of this tool to find all corresponding encoding information
What are the control characters in ASCII used for?
Control characters (0–31) are mostly no longer used directly in modern systems, but they are still important historically and in specific scenarios:
- NUL (0): String terminator in C language
- BEL (7): The terminal beeps
- BS (8): Backspace key
- TAB (9):Tab character (indentation)
- LF (10)：Unix/Linux newline
- CR (13): Enter
- ESC (27): Escape key, commonly used in terminal control sequences
- DEL (127): Delete key

These characters are still active in areas such as network protocols, serial communications, and printer control.
What is a Code Page?
Code Page is a character encoding table defined by IBM and Microsoft, which is used to specify the display mode of the 128–255 range (Extended ASCII). Different languages use different Code Pages, for example:
- CP437: IBM PC native code page (contains frame-drawing characters)
- Windows-1252: Western European (replaces ISO-8859-1)
- CP850: Latin-1 (for DOS)
Before Unicode became popular, Code Page was the only way to handle multiple languages.
What is the NUL character (0x00)?
NUL (Null character) is the control character of ASCII code 0. It does not mean "blank" or "space", but "no characters". In the C language, NUL is used as the end-of-string marker (null-terminator). In binary files, NUL is often used as padding or delimiter. Be careful not to confuse it with the C language's NULL (null pointer), which is completely different.
Why is 'A' 65? Isn't this decided casually?
The encoding sequence of ASCII is logical:
- Number (0–9): Encoding 48–57 (0x30–0x39), convenient programs can quickly convert to numerical values by subtracting 48
- Uppercase letters (A–Z): Encoding 65–90 (0x41–0x5A)
- Lowercase letters (a–z): Encoding 97–122 (0x61–0x7A)

There is a fixed difference of 32 (0x20) between uppercase and lowercase letters, which makes uppercase and lowercase conversion only require bit operations: lowercase = uppercase | 0x20, uppercase = lowercase & ~0x20. This design was critical in the early days of extremely limited memory and CPU resources.
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