Chmod Calculator

Calculate the octal and symbolic chmod permission string from checkboxes — no more mental math to figure out that read+write+execute for owner is a 7.

	Read	Write	Execute
Owner
Group
Others

755

Octal (chmod 755)

rwxr-xr-x

Symbolic

What this means

Owner: read, write, execute
Group: read, execute
Others: read, execute

Common presets

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Why use Chmod Calculator?

Unix file permissions are simple in concept — read, write, execute, for owner, group, and others — but the octal notation (755, 644, and so on) obscures that simplicity behind a small piece of mental arithmetic: each permission maps to a bit value (4/2/1) that gets summed per group. It's fast once memorized, easy to get wrong before that. This calculator works in both directions: check the boxes for the permissions you want and read off the octal and symbolic notation instantly, or start from a common preset (755 for scripts, 644 for regular files, 600 for private keys) and see exactly what it grants.

Key benefits

Instant octal and symbolic output together
6 common presets included
Plain-English breakdown of what each digit means
Free, no install required

Features

Checkbox-driven permission builder
Octal (chmod 755) and symbolic (rwxr-xr-x) formats
Common presets: 755, 644, 777, 700, 600, 664

Popular use cases

Setting the correct permissions for a web server file or directory
Understanding what a chmod command found in a script or tutorial actually does
Converting between octal and symbolic permission notation
Learning Unix file permissions

How to use Chmod Calculator

1
Check the permissions you want
Read, write, execute for owner, group, and others.
2
Read the results
Octal (like 755) and symbolic (like rwxr-xr-x) shown instantly.
3
Or start from a preset
Common permission sets like 755, 644, or 600.

Frequently asked questions

How is the octal number calculated?

Each permission type has a value: read=4, write=2, execute=1. Add them up per group — read+write+execute = 4+2+1 = 7, read+execute (no write) = 4+1 = 5, read only = 4. Three digits cover owner, group, and others in that order.

What does chmod 755 mean?

Owner gets read+write+execute (7), while group and others get read+execute but not write (5 each) — the standard permission set for executable scripts and directories that others need to run or browse but not modify.

What's the difference between chmod 644 and 664?

644 gives the owner read+write, while group and others get read-only. 664 extends write access to the group as well, common for files a team collaboratively edits on a shared server.

Last reviewed: September 2026

What this means

Common presets

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