🔐 Chmod Calculator

By ToolNimba Editorial Team · Updated 2026-06-19

This chmod calculator converts file permissions between the checkbox view, the octal number (like 755), and the symbolic string (like rwxr-xr-x). Tick read, write, and execute for the owner, the group, and everyone else, and the octal and symbolic values update at once. It also works the other way: type an octal value and the boxes tick themselves, so you can read off the exact chmod command to run.

What is the Chmod Calculator?

On Unix and Linux systems every file and directory carries a set of permissions that decide who may read it, write to it, or run it. Permissions are split across three classes: the owner (the user who owns the file), the group (a set of users), and other (everyone else). Each class has three independent permission bits: read (r), write (w), and execute (x). That gives nine bits in total, which is why a permission string looks like rwxr-xr-x.

The chmod command sets these bits. The quickest way to express them is octal, where each class becomes a single digit from 0 to 7. The trick is that read is worth 4, write is worth 2, and execute is worth 1, and you add the values you want. So rwx is 4 plus 2 plus 1, which is 7, and r-x is 4 plus 1, which is 5. Stack the three digits in owner, group, other order and 755 means rwxr-xr-x.

The symbolic form (the rwxr-xr-x string) is what you see in a long directory listing. It is exactly the same information shown as letters instead of numbers, with a dash standing for a permission that is switched off. Knowing both notations is useful: octal is compact for typing a chmod command, while the symbolic string is easier to scan when you are reading the output of a listing and checking what is allowed.

When to use it

Working out the octal number to pass to chmod when you only know which boxes you want ticked.
Reading a symbolic string like rwxr-xr-x from a directory listing and turning it back into a number.
Setting safe permissions for web files, such as 644 for pages and 755 for folders and scripts.

How to use the Chmod Calculator

Tick the read, write, and execute boxes you want for the owner, the group, and other.
Read off the octal value (for example 755) and the symbolic string (for example rwxr-xr-x).
Or type an octal value into the box and watch the checkboxes update to match.
Copy the ready-made chmod command and run it against your file or folder.

Formula & method

Each class digit = (read ? 4 : 0) + (write ? 2 : 0) + (execute ? 1 : 0). Octal = owner digit, group digit, other digit. So rwx = 4+2+1 = 7 and r-x = 4+0+1 = 5.

Worked examples

You want the owner to read, write, and run a script, while group and other may read and run it.

Owner rwx = 4 + 2 + 1 = 7
Group r-x = 4 + 0 + 1 = 5
Other r-x = 4 + 0 + 1 = 5
Combine the digits in owner, group, other order: 755

Result: Octal 755, symbolic rwxr-xr-x, command chmod 755 file

A plain web page that everyone may read but only the owner may edit.

Owner rw- = 4 + 2 + 0 = 6
Group r-- = 4 + 0 + 0 = 4
Other r-- = 4 + 0 + 0 = 4
Combine the digits: 644

Result: Octal 644, symbolic rw-r--r--, command chmod 644 file

A private key file that only the owner may read and write.

Owner rw- = 4 + 2 + 0 = 6
Group --- = 0
Other --- = 0
Combine the digits: 600

Result: Octal 600, symbolic rw-------, command chmod 600 file

Permission bit values

Permission	Letter	Octal value
Read	r	4
Write	w	2
Execute	x	1
No access	-	0

Common chmod values and what they mean

Octal	Symbolic	Typical use
755	rwxr-xr-x	Folders and scripts: owner full, others read and run
644	rw-r--r--	Regular files like web pages and documents
600	rw-------	Private files such as keys, owner only
700	rwx------	Private folders and scripts, owner only
777	rwxrwxrwx	Full access for everyone (rarely a good idea)
640	rw-r-----	Owner edits, group reads, other no access

Common mistakes to avoid

Using 777 by default. Setting 777 gives every user full read, write, and execute access. It often hides a real permission problem and is a security risk, especially on a web server. Prefer 755 for folders and 644 for files.
Confusing the digit order. The three digits are always owner, then group, then other. Writing 745 when you meant 754 silently changes who can do what, so double-check the order before running chmod.
Forgetting that folders need execute. On a directory the execute bit means the right to enter it and access its contents. A folder with 644 cannot be opened, so directories usually need 755 rather than 644.
Adding execute to data files that do not need it. Plain files like images, text, or HTML do not need the execute bit. Marking them executable adds nothing useful and can make audits noisier, so 644 is the right choice for them.

Glossary

chmod: The Unix command (short for change mode) that sets the read, write, and execute permissions on a file or directory.
Octal notation: A base-8 way of writing permissions where each class is one digit from 0 to 7, formed by adding read (4), write (2), and execute (1).
Symbolic notation: The letter form of permissions, such as rwxr-xr-x, where a dash means the permission is switched off.
Owner, group, other: The three permission classes: the user who owns the file, a group of users, and everyone else on the system.
Execute bit: On a file it allows the file to be run as a program; on a directory it allows the directory to be entered and its contents accessed.

Frequently asked questions

What does chmod 755 mean?

It gives the owner read, write, and execute (the 7), and gives the group and other read and execute (the two 5s). In symbolic form that is rwxr-xr-x. It is a common setting for folders and scripts that everyone may read and run but only the owner may change.

How is the octal permission number calculated?

Each class (owner, group, other) is one digit. Add 4 for read, 2 for write, and 1 for execute, for the permissions you want on. So rw- is 4 plus 2 which is 6, and the three digits together form the octal value such as 644.

What is the difference between 644 and 755?

644 (rw-r--r--) lets the owner read and write while others can only read, which suits regular files. 755 (rwxr-xr-x) adds the execute bit for everyone, which directories and scripts need so they can be entered or run.

Is chmod 777 safe?

Usually not. 777 grants every user full read, write, and execute access, which on a shared system or web server is a security risk. It often masks an ownership problem. Use the least access that works, typically 755 for folders and 644 for files.

What does the execute bit do on a folder?

On a directory the execute bit means the right to enter it and reach the files inside, rather than the right to run it as a program. That is why directories normally need execute permission (for example 755) even though they are not programs.

Can I convert a symbolic string back to a number?

Yes. Read it in three groups of three. For each group, add 4 for r, 2 for w, and 1 for x, treating each dash as 0. So rwxr-xr-x becomes 7, 5, 5, which is 755. This calculator does the conversion in both directions for you.

Class	Read (4)	Write (2)	Execute (1)
Owner
Group
Other