Chmod Calculator

What this tool does

This tool converts a Unix file permission mode between its two common representations: the 3-digit octal form (like 755) used with the chmod command, and the 9-character symbolic form (like rwxr-xr-x) shown by ls -l. Enter either one and get both back, along with a plain breakdown of exactly what the owner, group and everyone else ("other") are permitted to do.

When you need it

• Translating ls -l output into the numeric mode you actually need to type into a chmod command, without mentally converting three binary triplets by hand.
• Double-checking that a mode you're about to apply — in a script, a deployment config, or a manual chmod — actually grants the permissions you intend, before running it.
• Reviewing a Dockerfile, deployment script or infrastructure config that sets file permissions, to confirm a mode like 640 or 755 means what you think it means.
• Learning or teaching how Unix permissions work, where seeing the same mode broken out into read/write/execute for each of the three scopes makes the underlying bit math concrete.

How the conversion works

Every Unix file mode is really three independent permission sets — for the file's owner, its group, and everyone else — each expressed as a combination of read, write and execute. In octal, each set collapses to a single digit from 0–7: read is worth 4, write is worth 2, execute is worth 1, and the digit is their sum for whichever permissions are granted. In symbolic form, each set is written as three characters, r, w and x in that fixed order, with a - standing in for any permission that isn't granted. 755 and rwxr-xr-x describe exactly the same mode: the owner gets all three (7 = 4+2+1, rwx), while group and other each get read and execute but not write (5 = 4+1, r-x).

Reading the three scopes

The three digits, or three-character triplets, always apply in the same fixed order: owner first, then group, then other. This matters because a common mistake is assuming the first number always means "everyone" or misreading which scope a restrictive digit applies to — a mode like 700 grants full access to the owner and nothing at all to anyone else, while 077 (rare in practice) would do the reverse.

Common modes and what they mean

644 is the default for most regular files: the owner can read and write, everyone else can only read. 755 is standard for executable scripts and directories: the owner has full control, everyone else can read and execute (or, for a directory, list and enter it) but not modify. 600 restricts a file — often something sensitive like a private key — to the owner alone, with no access for anyone else.

What you can type

A 3-digit octal mode (755), the same with a leading zero (0755, as people often type it), a 9-character symbolic mode (rwxr-xr-x), or a full ls -l permission string with its file-type character (-rwxr-xr-x, drwxr-xr-x). A mode with a special bit (4755, 1777, or symbolic rwsr-xr-x) is refused with a message saying so, rather than being silently converted to the wrong value.

Limits

This tool covers the standard owner/group/other permission bits only. It doesn't calculate the special setuid, setgid or sticky bits (the optional 4th octal digit), which cover a narrower set of use cases than the base three-scope permissions this handles.