What does chmod 755 mean?

755 gives the owner read, write and execute (7 = 4+2+1), and the group and other read and execute only (5 = 4+1). It is the typical permission for directories and executable scripts.

How is the octal value calculated?

Each scope adds read (4), write (2) and execute (1). So read plus write is 6, read plus execute is 5, and all three is 7. The three digits are owner, group and other in that order.

What does chmod 644 mean?

644 gives the owner read and write (6 = 4+2), and the group and other read only (4). It is the standard permission for regular files that should not be executable.

What is the difference between octal and symbolic notation?

Octal uses three digits (owner, group, other), each a sum of read 4, write 2 and execute 1 — for example 755. Symbolic spells out the same bits as rwxr-xr-x. Both describe identical permissions.

Does this tool send my permissions anywhere?

No. The calculator runs entirely in your browser, so nothing you select or copy is uploaded.

Chmod Calculator — Gera Tools

The Unix chmod command sets file permissions, but its octal numbers are easy to get wrong. This calculator lets you tick read, write and execute for owner, group and other, then shows the octal value, the symbolic notation (rwxr-xr-x) and a ready-to-run chmod command. It works both ways — apply a preset and watch the checkboxes update.

How it works

Each of the three scopes (owner, group, other) gets one octal digit, formed by adding the permission bits it has: read = 4, write = 2, execute = 1. So read+write is 6, read+execute is 5, and all three is 7. The three digits are concatenated in the order owner-group-other. Symbolic notation expresses the same bits as a 9-character string, with a letter (r, w, x) where the bit is set and a dash where it is not.

Permission	Octal	Symbolic
read	4	r—
read + write	6	rw-
read + execute	5	r-x
read + write + execute	7	rwx

Example

For owner = read+write+execute, group = read+execute, other = read+execute:

owner 4+2+1 = 7, group 4+1 = 5, other 4+1 = 5 → 755 → rwxr-xr-x → chmod 755 filename

This is the usual permission for directories and executable scripts. Presets cover 644 for files, 755 for executables and directories, 600 for private files, and 777 for full access. Everything runs in your browser; nothing is uploaded.