🔐 Chmod Calculator

Convert between numeric (e.g. 755) and symbolic (e.g. rwxr-xr-x) Unix file permission notation. Check the boxes or type either format — both stay in sync.

Owner

Group

Others

Read

Write

Execute

Numeric

Symbolic

How the three digits are worked out

Each digit is one class of user - owner, group, others - and is the sum of three bits: read 4, write 2, execute 1. Nine checkboxes, nine bits, one octal digit per column of three.

read 4 + write 2 + execute 1 = 7  rwx
read 4 +           execute 1 = 5  r-x
read 4 + write 2             = 6  rw-

755 = rwx r-x r-x    644 = rw- r-- r--

Typing in either box, or ticking any checkbox, rewrites the other two views at once and prints the chmod 755 filename line ready to paste into a shell.

What each field will accept

Numeric takes three or four octal digits. A fourth leading digit is accepted but then discarded, so 4755 collapses to 755 - setuid, setgid and the sticky bit are not modelled here.
Symbolic takes exactly nine characters of r, w, x and -. The ten-character string from ls -l starts with a file-type flag, so paste rwxr-xr-x, not -rwxr-xr-x.

On a directory, execute means "may enter and traverse", not "may run". A directory at 644 lists nothing useful; directories almost always want 755.

Frequently asked questions

What does chmod 755 mean?

The owner may read, write and execute; group and others may read and execute but not change anything. It is the normal setting for directories, scripts and anything a web server has to serve.

What is the difference between 644 and 755?

Only the execute bit. 644 is a plain data file the owner can edit and everyone can read; 755 adds execute for all three classes, which a file needs to run as a program and a directory needs to be opened at all.

What does the leading digit in 4755 do?

It carries setuid 4, setgid 2 and the sticky bit 1 - so 4755 runs as the file's owner and 1777 is the classic /tmp. This calculator ignores that digit and shows the permission bits only.