ASCII to Binary Converter
Turn plain ASCII text into 8-bit binary bytes, with a clear error for anything outside the ASCII table.
Going the other way? Use the binary to ASCII converter.
To convert ASCII to binary, look up each character's code number and write it as an 8-bit byte. Capital C is code 67, which becomes 01000011. String the bytes together in order and you have the binary form of your text. The tool above does it live as you type.
How it works
ASCII assigns every one of its 128 characters a fixed number between 0 and 127. Encoding is two moves per character: find the number, write it in base 2 with enough leading zeros to fill eight digits.
Worked example with the word "Cat". C has code 67. In binary that is 01000011, because the switched-on places are worth 64 + 2 + 1. Lowercase a is 97, giving 01100001, and t is 116, giving 01110100. Put the three bytes in order:
01000011 01100001 01110100
Three characters, three bytes, twenty-four digits. Every ASCII character costs exactly one byte, so you can size a message at a glance: digits divided by eight equals characters.
This page is deliberately strict about what counts as ASCII. Type an é, a curly quote, or an emoji and you get an error naming the character rather than a silently wrong byte. That strictness is useful when the output has to feed a system that expects pure ASCII, like old protocols, embedded devices, or homework graders. If you want those richer characters encoded rather than rejected, the text to binary converter handles the full UTF-8 range.
One reassuring detail: for the characters ASCII does cover, ASCII and UTF-8 agree exactly, so bytes made here decode correctly everywhere.
ASCII table excerpt: a to j
| Character | Decimal | Binary |
|---|---|---|
| a | 97 | 01100001 |
| b | 98 | 01100010 |
| c | 99 | 01100011 |
| d | 100 | 01100100 |
| e | 101 | 01100101 |
| f | 102 | 01100110 |
| g | 103 | 01100111 |
| h | 104 | 01101000 |
| i | 105 | 01101001 |
| j | 106 | 01101010 |
Lowercase letters start at code 97 and count up one per letter. Capitals sit exactly 32 lower, one binary place value, which is why case flips by toggling a single bit.
FAQ
How do I convert ASCII to binary?
Look up each character's ASCII code, then write that code in base 2 padded to eight digits. Capital C has code 67, which becomes the byte 01000011. Repeat for every character in order, so "Cat" comes out as the three bytes 01000011 01100001 01110100.
Why does an accented letter or emoji show an error?
ASCII only defines 128 characters: unaccented English letters, digits, punctuation, and control codes. An é or an emoji has no ASCII code at all, so this page reports exactly which character has no encoding. For those characters, use the text to binary converter in UTF-8 mode instead.
Is ASCII binary the same as UTF-8 binary?
For the 128 ASCII characters, yes, byte for byte. UTF-8 was designed so those characters keep their exact ASCII codes in a single byte. "Cat" produces 01000011 01100001 01110100 in both encodings. The two only differ on characters beyond ASCII, which UTF-8 spells with two to four bytes.