Chmod Calculator — Linux File Permissions Made Simple
Calculate Linux and Unix file permissions visually with this free online chmod calculator. Check read, write, and execute boxes for owner, group, and others, and instantly get the octal number (like 755 or 644) and the symbolic notation (like rwxr-xr-x) — or paste either format to decode what it grants.
Permissions guard every file on Linux, macOS, and your servers, and getting them wrong swings between broken deployments (scripts that won't execute) and security holes (world-writable configs). This calculator translates between the checkbox mental model, octal digits, and symbolic strings so you always know exactly what a chmod command will do.
How to Calculate Chmod Permissions
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Tick the permission boxes
Enable read, write, and execute independently for owner, group, and others.
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Read the octal value
The three-digit number (e.g. 755) updates live — each digit is the sum of read (4), write (2), and execute (1).
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Check the symbolic form
The rwxr-xr-x string mirrors your selection, matching what ls -l displays.
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Copy the command
Use the resulting value in chmod, e.g. chmod 644 config.yml, on your server or in your scripts.
Features of the Chmod Calculator
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Three-way translation
Checkboxes, octal (755), and symbolic (rwxr-xr-x) stay in sync — enter any one, read the others.
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Decode existing permissions
Paste a value from ls -l or a tutorial and see exactly which users can do what.
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Owner / group / others breakdown
The permission model is laid out visually, making the three permission classes obvious.
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Prevents dangerous mistakes
See at a glance when a setting makes files world-writable before you run it in production.
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Instant and offline-capable
Pure client-side calculation — works even without a connection once loaded.
Frequently Asked Questions
What does chmod 755 mean?
Owner: read, write, execute (7 = 4+2+1). Group and others: read and execute (5 = 4+1). It is the standard permission for directories and executable scripts — everyone can run and read, only the owner can modify.
What is the difference between chmod 644 and 755?
644 (rw-r--r--) has no execute bits — right for regular files like configs and HTML. 755 (rwxr-xr-x) adds execute for everyone — required for scripts, binaries, and directories (execute on a directory means permission to enter it).
How are the octal digits calculated?
Each digit sums the permissions it grants: read = 4, write = 2, execute = 1. So rwx = 7, rx = 5, rw = 6, r = 4. Three digits cover owner, group, and others in that order.
Why is chmod 777 dangerous?
777 lets every user on the system read, modify, and execute the file. On servers this invites tampering and is a classic security-audit failure. Prefer the narrowest permissions that work — usually 755 for directories and 644 for files.
What does execute permission mean on a directory?
On directories, execute means 'can enter and traverse' — without it, users cannot cd into the directory or access files inside it even if the files themselves are readable.