About chmod Calculator
Every file and directory on a Unix system carries a permission mask made of three identical groups — owner, group and everyone else — and each group can be granted or denied three abilities: reading, writing and executing. The chmod Calculator turns those nine decisions into the three-digit octal number that the chmod command accepts, so you do not have to work out the arithmetic in your head.
The arithmetic itself is simple and worth understanding because it explains why the result looks the way it does. Read is worth 4, write is worth 2 and execute is worth 1, and each digit is the sum of whichever of the three are turned on. Owner read and write is 4 plus 2, or 6; owner read only is 4; read plus execute is 5. The three digits are then written in order — owner first, then group, then everyone else.
The result updates as you tick and untick the boxes, so you can watch a mode like 644 take shape. Two values are worth recognising because they appear constantly: 644, the default for ordinary files, gives the owner read and write with everyone else read-only; and 755, the default for directories and executables, adds execute for every group so the item can be opened or run.
How to use chmod Calculator
- 1 Tick or untick read, write and execute for the owner, group and everyone else.
- 2 Read the three-digit octal value that updates as you change the boxes.
- 3 Use that value in a chmod command, for example chmod 644 filename.
Frequently asked questions
Why is the result three digits?
Because permissions are grouped three ways — owner, group and everyone else — and each group contributes one digit from 0 to 7. Read, write and execute map to 4, 2 and 1, so a digit is simply the sum of the permissions turned on for that group.
What does 644 mean?
The owner can read and write (4 plus 2 equals 6), while the group and everyone else can only read (4). It is the standard mode for ordinary files — the owner edits, everyone else reads.
What does 755 mean?
The owner has read, write and execute (4 plus 2 plus 1 equals 7), and the group and everyone else have read and execute (4 plus 1 equals 5). It is the normal mode for directories and executable files, which need the execute bit for anyone to enter or run them.
How do I get read, write and execute for the owner only?
Tick all three owner boxes and untick everything else. That gives owner 7, group 0 and everyone else 0 — the mode 700, which keeps the item completely private to the owner.
Free, online, and private
Free to use
chmod Calculator is completely free. There is no account to create, no login, and no hidden charge or usage limit.
Runs online in your browser
It is a free online tool that runs entirely in your browser. Nothing to download or install — open the page and start using it right away.
Your data stays private
All processing happens locally on your device. Your input is never uploaded, stored, or tracked, so it never leaves your browser.
How chmod Calculator behaves in detail
These are the specifics of this implementation — the exact ranges, defaults and fixed settings you are working with.
| Parameter | Value |
|---|---|
| Input model | 9 independent checkboxes — read, write and execute for owner, group and other — so there is no symbolic or octal text field |
| Digit weights | read adds 4, write adds 2, execute adds 1, summed per class |
| Output | the literal string `chmod OGO` on the first line, then `Owner: O Group: G Other: O` on the second |
| Every digit is always emitted | a class with no boxes ticked contributes 0, so the output is always three digits — never 7 or 75 |
| Defaults | Owner read and write are ticked, plus Other read — the form opens on 644 |
| Live | kind is `form`, not `text` — the result recomputes on every checkbox change and there is no run button |
Compiled from the implementation of this tool and checked against it by itoolnet.
What chmod Calculator does not do
Knowing the edges of a tool saves more time than another list of its features. These are the cases where it will not do what you might expect.
- The setuid, setgid and sticky bits are unreachable. The ninth weight of the octal form — 4 for setuid, 2 for setgid, 1 for sticky — has no checkbox anywhere, so 4755, 2755 and 1777 cannot be produced or checked on this page.
- The leading zero is dropped. Four-digit octal such as 0644 and 0755 is written back as 644 and 755, and someone who is about to type the value into a script that expects four digits gets an answer that is a character short of what they need.
- A class with nothing ticked emits a 0 rather than being treated as a mistake, so one stray click on Owner read produces `chmod 044` with no warning — and 044 is a perfectly valid octal number that means something on disk.
- Nothing but the number comes back. There is no symbolic form such as u=rw,go=r, no reverse lookup of the value against the filesystem, and no explanation of what each digit allows — the page assumes you already know how the three triads map onto files and directories.
Tested and documented by itoolnet, the team that builds and maintains this site.