Chmod Calculator
Convert Unix file permission checkboxes (read/write/execute for owner, group and others) into the numeric chmod value and symbolic notation, plus a ready-to-run chmod command.
Input
Owner
Group
Others
Output
Guides
What does this chmod calculator do?
Tick the read, write and execute boxes for the file's owner, group and others, and the tool instantly converts your selection into the numeric (octal) chmod value, the symbolic permission string, and a ready-to-run chmod command you can paste straight into a terminal.
How Unix permissions work
Every file and directory on a Unix-like system (Linux, macOS, BSD) carries three permission bits for three separate audiences:
- Owner — the user who owns the file.
- Group — members of the file's group.
- Others — everyone else.
Each audience gets three possible permissions:
- Read (4) — view a file's contents, or list a directory.
- Write (2) — modify a file, or add/remove entries in a directory.
- Execute (1) — run a file as a program, or enter (
cdinto) a directory.
The three bits for one audience are summed into a single digit: read + write + execute. rwx is 4 + 2 + 1 = 7, r-x is 4 + 0 + 1 = 5, r-- is 4 + 0 + 0 = 4. Stack the owner, group and other digits together and you get the familiar three-digit octal number, e.g. 754.
The same permissions can also be written symbolically as a 9-character string — three rwx-style triplets, one per audience, with a dash standing in for any bit that's off. 754 is rwxr-xr--.
Common chmod values
- 644 (
rw-r--r--) — the standard for regular files: the owner can read and write, everyone else can only read. Good default for documents, configs and web assets. - 755 (
rwxr-xr-x) — the standard for directories and executable scripts: the owner can read, write and execute; everyone else can read and execute (or list/enter, for a directory) but not modify. - 777 (
rwxrwxrwx) — full read/write/execute for everyone. Rarely appropriate — it lets any user on the system modify or replace the file, which is a common source of security issues on shared servers. - 600 (
rw-------) — owner-only read/write, no access for anyone else. Used for private keys, credentials and other sensitive files.
How to use it
- Check the boxes that match the permissions you want for owner, group and others.
- Read off the numeric value (e.g.
754) and the symbolic string (e.g.rwxr-xr--) instantly — the result updates as you click. - Copy the generated
chmod <value> filenamecommand and swap in your real filename.
FAQ
Why does chmod use octal (base-8) numbers?
Because each permission group is exactly 3 bits, and 3 bits range from 000 to 111 in binary — 0 to 7 in octal. One octal digit maps perfectly onto one audience's read/write/execute state.
What does a fourth leading digit mean, like chmod 4755?
That's a special permission bit (setuid, setgid or sticky) prepended to the normal three digits. This calculator focuses on the standard owner/group/other permissions covered above.
Can I go the other direction, from a number back to checkboxes? Not yet — this tool converts checkbox selections into the numeric and symbolic forms. To read an existing octal value, split it into three digits and match each against the read=4/write=2/execute=1 breakdown above.
Privacy
All conversion happens locally in your browser. No file names, paths or permissions are ever sent anywhere.
Use it from code
From 3 credits per callREST API
curl -X POST https://api.iotools.cloud/v1/tool/chmod-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"ownerRead": "true",
"ownerWrite": "true",
"ownerExecute": "true",
"groupRead": "true",
"groupWrite": "",
"groupExecute": "true",
"otherRead": "true",
"otherWrite": "",
"otherExecute": ""
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `chmod-calculator` tool (Chmod Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.