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Chmod calculator

Convert Unix file permissions between octal and rwx notation with a full breakdown.

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Chmod calculator
Unix file permissions look cryptic until you see the arithmetic behind them. Each of the three digits in a chmod value is a simple sum: read is 4, write is 2, execute is 1. So 7 means read plus write plus execute, 5 means read plus execute, and 755 grants the owner full control while the group and everyone else may read and run the file. This calculator translates in both directions — paste octal values like 755 or 0644 and get the rwx notation, or paste a string like rwxr-xr-x (with or without the leading file-type character from ls -l) and get the octal value back.
The breakdown view spells out exactly what the owner, the group and others may do, notes special bits such as setuid, setgid and the sticky bit (4755, 2755, 1777), and prints the ready-to-use chmod command. Switch to conversion only when you just need the equivalent notation, one line per permission. Every line is processed independently, so you can convert a whole list at once — a typo in one line produces a calm message in place and never stops the rest.
A handful of values covers most real work: 644 for ordinary files, 755 for directories and scripts, 600 for private keys and secrets. Avoid 777 — a world-writable file can be modified or replaced by any user on the machine, which is rarely what you want and a classic security-audit finding.
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FAQ
How do the octal digits work?
Each digit is the sum of read (4), write (2) and execute (1) for one class of users, in the order owner, group, others. 755 is therefore rwx for the owner and r-x for the group and others.
What do 4755, 2755 and 1777 mean?
A fourth leading digit sets the special bits: setuid is 4, setgid is 2 and the sticky bit is 1. In rwx notation they show as s or t in the execute position — lowercase when execute is also set, uppercase (S, T) when it is not.
Why is chmod 777 a bad idea?
It makes the file readable, writable and executable for everyone. Any user or compromised process on the machine can overwrite it, which turns a harmless file into an attack vector. Use 644 or 755 and widen permissions only when something genuinely fails without it.
Can I convert many permissions at once?
Yes. Put one permission per line — octal and symbolic forms can be mixed freely. Invalid lines are reported in place and the remaining lines still convert.
Is my input uploaded anywhere?
No. The calculator runs entirely in your browser and your input never leaves your device.