How do I use chmod on the command line?

Run chmod followed by the permission value and filename. For example: chmod 755 script.sh makes a script executable by everyone. chmod 644 file.txt gives the owner write access and everyone else read-only.

How is the octal number calculated?

Each permission group (owner, group, other) is a sum of its bits: read=4, write=2, execute=1. So rwx=7, rw-=6, r-x=5, r--=4, ---=0. A permission of 755 means owner=7 (rwx), group=5 (r-x), other=5 (r-x).

Can I use chmod with symbolic notation instead of numbers?

Yes. chmod u+x file.sh adds execute for the owner. chmod go-w file removes write from group and others. chmod a+r file adds read for all. Symbolic notation is useful for adding or removing specific permissions without resetting others.

Why does the calculator not accept 4755?

The first digit of a four-digit mode holds the special bits: 4 is setuid, 2 is setgid and 1 is the sticky bit, so 4755 is setuid plus 755. This calculator covers the nine read, write and execute bits only and shows a hint when you type a mode like that. Leading zeros are fine: 0755 and 00755 are read as 755.

Chmod permissions calculator

Enter a chmod octal value (like 755 or 644) or click the permission checkboxes to build a permission set. The tool shows both the numeric value and the symbolic rwx notation.

How it works

The tool converts between octal, symbolic, and binary permission representations using pure JavaScript bit arithmetic. No library required. Checking a box sets the corresponding bit; typing an octal value like 755 reverses the process to tick the right boxes.

Processing runs in your browser

All calculations happen locally in the page. Our servers are not involved at any point.

Related operations

For subnet math like host counts and netmasks, try the CIDR calculator. To convert numeric permission bits between bases, use the number base converter. For testing permission patterns in path strings, see the regex tester.

Frequently asked questions

How do I use chmod on the command line?: Run chmod followed by the permission value and filename. For example: chmod 755 script.sh makes a script executable by everyone. chmod 644 file.txt gives the owner write access and everyone else read-only.
How is the octal number calculated?: Each permission group (owner, group, other) is a sum of its bits: read=4, write=2, execute=1. So rwx=7, rw-=6, r-x=5, r--=4, ---=0. A permission of 755 means owner=7 (rwx), group=5 (r-x), other=5 (r-x).
Can I use chmod with symbolic notation instead of numbers?: Yes. chmod u+x file.sh adds execute for the owner. chmod go-w file removes write from group and others. chmod a+r file adds read for all. Symbolic notation is useful for adding or removing specific permissions without resetting others.
Why does the calculator not accept 4755?: The first digit of a four-digit mode holds the special bits: 4 is setuid, 2 is setgid and 1 is the sticky bit, so 4755 is setuid plus 755. This calculator covers the nine read, write and execute bits only and shows a hint when you type a mode like that. Leading zeros are fine: 0755 and 00755 are read as 755.

Last reviewed September 30, 2026

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	Read	Write	Execute	Value
Owner				7 (rwx)
Group				5 (r-x)
Other				5 (r-x)