# Chmod Permission Calculator

> Convert octal or symbolic chmod modes into readable Unix permissions.

- Page: https://decoder.tools/chmod-calculator
- Category: Network, System & Packets
- Status: live, runs in the browser
- Last reviewed: 2026-10-23

A chmod calculator converts between the octal notation of Unix file permissions (755) and their symbolic form (rwxr-xr-x), showing what the owner, group and other users are each allowed to do with a file.

## Example

```text Input
0644
```

```text Output
rw-r--r--
Owner: rw-  (6)
Group: r--  (4)
Others: r--  (4)
```

## What is the Chmod Permission Calculator?

Unix permissions are nine bits in three groups of three: read, write and execute for the owner, the group and everyone else. Each group is one octal digit, because read is 4, write is 2 and execute is 1 — so 7 is all three, 6 is read plus write, 5 is read plus execute.

That gives the two modes you type most often. 644 (rw-r--r--) is the standard for a file: the owner can edit it, everyone else can read it. 755 (rwxr-xr-x) is the standard for a directory or a script: the owner can modify, everyone can enter or execute. On a directory the execute bit means 'may traverse into', which is why a directory with 644 is unusable.

A fourth leading digit sets the special bits: 4 for setuid (run as the file's owner), 2 for setgid (run as the group, or inherit the group on new files in a directory) and 1 for the sticky bit, which on /tmp stops users deleting each other's files. Setuid on a writable binary is a privilege-escalation finding, not a configuration choice.

## How to use the Chmod Permission Calculator

1. Enter an octal mode such as 755, or a symbolic string such as rwxr-xr-x.
2. Read the equivalent notation and the per-class permission breakdown.
3. Check the special-bit digit if the mode has four digits.

## When to use it

- Working out the right mode for a deploy script or an uploaded file.
- Auditing an SSH key or config file that a service refuses to load.
- Explaining permission bits during code review or onboarding.

## Chmod Permission Calculator at a glance

| | |
|---|---|
| Bit values | read 4 · write 2 · execute 1 |
| 644 | rw-r--r-- — the normal file default |
| 755 | rwxr-xr-x — directories and executables |
| Special bits | 4 setuid · 2 setgid · 1 sticky (leading digit) |

## FAQ

### What does chmod 755 mean?

The owner may read, write and execute; group and others may read and execute but not write. It is the usual mode for directories and executable scripts.

### What is the difference between 644 and 755?

The execute bit. 644 is for ordinary files that shouldn't be run; 755 adds execute, which files need to be run as programs and directories need to be entered.

### Why does SSH reject my private key?

Because it is readable by others. SSH requires 600 (rw-------) on private keys and refuses to use anything more permissive.

### What is the sticky bit?

The leading 1 in a mode like 1777. On a shared directory such as /tmp, it means only a file's owner can delete it, even though everyone can write to the directory.