Ascii Binary Table

ASCII assigns a number from 0 to 127 to each letter, digit, punctuation mark and control code, and those numbers are what computers store in binary. This table lists all 128 codes with their decimal, hex, octal and 8-bit binary values, explains the control characters, and lets you type any text to see its codes — with printable charts in the pack.

How the ASCII table is organised

The layout has useful patterns. A digit’s code is 48 plus its value, so the low four bits of ‘7’ (0011 0111) are 0111 = 7. Uppercase and lowercase letters differ only in one bit (value 32): A is 0100 0001 and a is 0110 0001, which is why flipping bit 5 changes case.

Control characters you still meet

Most other control codes come from teleprinters and early data links and are rarely used directly today, though some still appear in serial communications and file formats.

ASCII, extended ASCII and Unicode

ASCII defines only 128 characters, which fit in 7 bits; stored in a byte, the top bit is 0. “Extended ASCII” is a loose name for various 8-bit code pages that used codes 128–255 for accented letters and symbols — ISO 8859-1 (Latin-1) and Windows-1252 are common examples, and they differ in places. Unicode now covers every writing system, and its most common encoding, UTF-8, keeps the 128 ASCII characters as single bytes with identical codes. Characters beyond ASCII take two to four bytes in UTF-8, which the text lookup shows.

Worked example

The text “Hi!” is three ASCII characters: H is 72 (0x48, 0100 1000), i is 105 (0x69, 0110 1001) and ! is 33 (0x21, 0010 0001). Stored as bytes, “Hi!” is 01001000 01101001 00100001. Changing H to lowercase h flips one bit: 0110 1000 (104). In HTML, the exclamation mark could also be written as the numeric entity !.

Line endings and invisible characters

Many “mysterious” text problems come from invisible ASCII codes. A file created on Windows ends each line with CR LF (13 10), while Linux and macOS use LF alone, so scripts sometimes fail with stray carriage returns. Tabs (9) and spaces (32) look alike but break tab-separated data. A zero byte (0) can cut off a string in older software. Paste suspicious text into the lookup box to reveal exactly which codes it contains.

Reading binary quickly

Split each byte into two groups of four bits (nibbles): each nibble is one hex digit. 0100 1000 is 4 and 8, so 0x48, which is 4 × 16 + 8 = 72. With a little practice, recognising the patterns for letters (010 or 011 at the start) and digits (0011) makes raw data dumps readable.

A short history of ASCII

ASCII — the American Standard Code for Information Interchange — was first published in 1963 and revised in the late 1960s, building on the codes used by teleprinters. It standardised how letters, digits and control signals were represented so that equipment from different manufacturers could exchange text. The international version, ISO 646, allowed some national variants, and 8-bit code pages later extended the range. Unicode, first published in 1991, kept ASCII as its first 128 code points, which is why ASCII still underpins almost all text on computers today.

ASCII in programming

Because letters are in order, sorting by code sorts uppercase letters before lowercase ones — a common surprise when sorting mixed-case text.

Using the table in class

• Encode a name in binary and swap with a partner to decode.
• Spot the pattern between uppercase and lowercase letters.
• Write a secret message using decimal codes.
• Discuss why control characters exist and which survive today.
• Compare ASCII with UTF-8 for accented letters and emoji.

The ASCII reference pack

The optional pack includes a one-page printable ASCII chart (decimal, hex, binary and character), a control character reference, a binary alphabet sheet for classroom activities and an encoding worksheet with answers. The searchable table on this page is free.

AI-assisted content

This page was drafted with AI assistance and reviewed by Kedop. Codes follow the ASCII (US-ASCII / ISO 646 IRV) standard.