CHMOD Calculator

About this tool

File permissions are a 9-checkbox grid pretending to be a number. This calculator syncs both representations live in both directions: tick read/write/execute for owner, group and others and watch the octal update, or type 755 and watch the boxes flip.

setuid, setgid and the sticky bit are supported, and common values get plain-language safety notes.

How to use it

Tick the permissions you want — the octal value updates instantly.
Or type an octal value (644, 755, 2775…) to set the boxes.
Read the breakdown table and the safety note.
Run the shown chmod command on your server.

Useful ways to apply it

Setting correct permissions on shared hosting (644 files, 755 folders).
Understanding what a permission number in a tutorial actually grants.
Configuring setgid on shared project directories.
Avoiding 777 — the calculator warns you why.

Worked example

Example input

Owner rwx, group r-x, others r-x

Expected output

Edge cases to check

Directories need execute permission to traverse.
setuid, setgid and sticky bits are separate from ordinary rwx mode.
Recursive chmod can apply inappropriate modes to files versus directories.

Known limitations

The calculator explains permission bits; it cannot determine the correct ownership, ACLs or security policy for your server.

How this tool was reviewed

Reviewed with common 600/644/755 modes and file-versus-directory caveats.

Last reviewed: September 3, 2026 · Maintainer: William

Standards and technical references

See the site-wide testing methodology for fixture categories, privacy checks and correction policy.

Frequently asked questions

What do 4, 2 and 1 mean?

Read=4, write=2, execute=1. Each digit is the sum for one audience: owner, group, others. 754 = rwx (7) for owner, r-x (5) for group, r-- (4) for others.

What are safe permissions for websites?

Typically 644 for files and 755 for directories. PHP files don't need execute permission — the web server reads them.

What is the fourth digit (like 2775)?

Special bits: setuid=4, setgid=2, sticky=1. Setgid on a directory makes new files inherit the directory's group — handy for shared deploy folders.