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Chmod Calculator

Calculate Unix file permission values visually.

How to Use

Use the interactive permission grid to toggle read (r), write (w), and execute (x) permissions for Owner, Group, and Others. Each checkbox represents one permission bit — check it to grant, uncheck to deny. A live preview shows the symbolic notation (e.g., rwxr-xr--) updating in real time.
Read the octal (numeric) chmod value calculated automatically from your selections. Each permission set maps to a digit: read=4, write=2, execute=1, summed for each of the three user classes. For example, rwx (4+2+1=7) for owner, r-x (4+0+1=5) for group, and r-- (4+0+0=4) for others gives chmod 754.
Copy the chmod command (e.g., chmod 755 script.sh) ready to paste into your terminal. The calculator also shows common presets — 777 (full access), 755 (standard for executables), 644 (standard for files), 600 (private key files) — with explanations of when to use each.

What do the three digits in chmod mean?: Each digit represents permissions for one user class: the first digit is for the file Owner (u), the second for the Group (g), and the third for Others/o (everyone else). Each digit is the sum of read (4) + write (2) + execute (1). So chmod 640 means: owner can read+write (6), group can read (4), others get no access (0).
What's the difference between symbolic and octal notation?: Symbolic notation uses letters: u/g/o for user classes and r/w/x for permissions, with + to add and - to remove (e.g., chmod u+x script.sh adds execute for owner). Octal (numeric) notation uses three digits as described above (e.g., chmod 755). Octal is more compact and widely used in scripts; symbolic is more expressive for incremental changes.
What permissions should I use for SSH private keys?: SSH requires private keys to be readable ONLY by the owner: chmod 600 ~/.ssh/id_rsa. The SSH client refuses to use keys with group or world-readable permissions. The corresponding public key should be 644. The .ssh directory itself should be 700. Our calculator highlights these security-critical permission patterns.