# Chmod calculator

> Work out Unix file permissions: tick read, write and execute for owner, group and others to get the octal (755) and symbolic (rwxr-xr-x) forms. Free.

Canonical: https://toolspace.tech/chmod-calculator/
Last updated: 2026-10-25

Tick read, write and execute for the owner, the group and everyone else to get the octal mode (755) and the symbolic form (rwxr-xr-x), or type either one to fill in the boxes. Includes setuid, setgid and sticky.

This is an interactive tool that runs in the browser: [open the Chmod calculator](https://toolspace.tech/chmod-calculator/) to use it. Nothing typed into it is uploaded.

## Worked example

A script everyone can run but only the owner can edit.

**octal**

```
755
```

**symbolic**

```
rwxr-xr-x
chmod 755 deploy.sh
chmod u=rwx,g=rx,o=rx deploy.sh
```

## Common mistakes

### chmod 777 to fix an error

It makes the file writable by every user and process on the machine. Find out which user needs access and grant only that.

### Directories without execute

A directory needs x to be entered. 644 on a directory lets you list names but not open the files inside.

### Recursive chmod on mixed trees

chmod -R 755 makes every file executable. Use find with -type f and -type d to set files and directories separately.

### Loose SSH key permissions

ssh refuses a private key that others can read. Keep keys at 600 and ~/.ssh at 700.

## How it works

1. **Set the permissions:** Tick the boxes, pick a preset like 644 or 755, or type an octal or symbolic mode. Everything stays in sync.
2. **Read what it means:** A plain explanation says who can read, change or run the file, and what the special bits do.
3. **Copy the command:** Copy chmod 755 file or the symbolic chmod u=rwx,g=rx,o=rx file, with your file name filled in.

## Questions

### What do the digits in 755 mean?

One digit each for the owner, the group and others. Each is the sum of read (4), write (2) and execute (1): 7 is rwx, 5 is r-x, 4 is r--, 6 is rw-.

### What’s the fourth digit in 4755 or 0755?

The special bits: 4 is setuid, 2 is setgid and 1 is sticky, added together. 0755 is the same as 755 with no special bits.

### What do s, S, t and T mean in ls -l?

They take the execute spot. A lowercase s or t means the special bit and execute are both set; uppercase S or T means the special bit is set without execute, which usually has no useful effect.

### Which permissions should I use?

Common choices are 644 for ordinary files, 755 for scripts and directories, and 600 or 700 for private files such as SSH keys. Avoid 777: it lets anyone on the system change the file.

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