Chmod Calculator
100% private — runs on your device, never uploaded. Works offline once loaded.
Tick read, write and execute for the owner, group and others to instantly get the octal notation, the symbolic rwx string and the ready-to-run chmod command — or type an octal like 755 to set the checkboxes.
How Unix file permissions work
Every file and directory on a Unix-like system (Linux, macOS, BSD) carries permissions for three identities: the owner (user), the group, and others (everyone else). Each identity can be granted three permissions: read (r), write (w) and execute (x). Read lets you view a file's contents or list a directory, write lets you modify it, and execute lets you run a file as a program or enter a directory.
The chmod command changes these bits. This calculator gives you the two notations chmod understands — numeric octal and symbolic rwx — plus the exact command, so you never have to compute the numbers by hand.
The octal math
Each permission has a numeric weight: read is 4, write is 2 and execute is 1. Adding the weights of the permissions you grant to one identity produces a single digit from 0 to 7. Three identities give a three-digit octal number, written owner-group-others.
So rwx is 4+2+1 = 7, r-x is 4+0+1 = 5, rw- is 4+2+0 = 6, and --- is 0. The familiar 755 therefore means rwx for the owner and r-x for group and others, while 644 means rw- for the owner and r-- for the rest.
- read (r) = 4
- write (w) = 2
- execute (x) = 1
- Sum per identity → one octal digit (0–7).
Reading the symbolic form
The symbolic notation is the nine-character string you see in ls -l output, such as rwxr-xr-x. It is simply the three permission triplets concatenated: the first three characters are the owner's r/w/x (a dash means the permission is denied), the middle three are the group's, and the last three are others'.
This tool builds that string directly from the checkboxes and keeps it in lockstep with the octal digits, so you can learn to read either notation at a glance. It also assembles the full command, e.g. chmod 755 filename, ready to paste into a terminal.
Common presets and cautions
A few values come up constantly: 644 (rw-r--r--) for regular files, 755 (rwxr-xr-x) for directories and executables, 600 (rw-------) for private files like SSH keys, and 700 for private directories. Recursive changes with chmod -R are powerful but blunt — applying 755 to a tree of data files needlessly makes them executable, so prefer targeted commands.
Be especially careful with 777 (rwxrwxrwx): it grants everyone full control and is almost never the right answer. If a script only works at 777, the real problem is usually ownership, not permissions. This tool shows you exactly what a value grants before you run it.
Frequently asked questions
What is the difference between octal and symbolic chmod?
They express the same permissions two ways. Octal (755) is a compact three-digit number; symbolic (rwxr-xr-x, or relative forms like u+x) spells out read/write/execute per identity. chmod accepts either.
Why is 755 so common for directories?
Directories need the execute bit to be entered and read to be listed. 755 gives the owner full control and lets group and others list and enter but not modify — a safe default for shared folders and web roots.
How do I make a file private?
Use 600 (rw-------) so only the owner can read and write it, which is what SSH insists on for private keys. Set the octal field to 600 to see the boxes and command update.
Can this tool convert a symbolic string to octal?
It converts in both directions between checkboxes and octal, and displays the symbolic string alongside. Set the boxes to match your rwx string and read off the octal, or type the octal to see the symbolic form.
What does the leading fourth digit in something like 4755 mean?
That extra digit encodes special bits (setuid, setgid, sticky). This calculator focuses on the standard three permission digits; if you enter a four-digit octal it uses the last three.
Is 777 ever a good idea?
Almost never. It lets any user read, write and execute the file, which is a security risk. If something only works at 777, fix file ownership or the specific missing bit instead.
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