Chmod Calculator
Work out a Unix file permission number by toggling read, write, and execute for owner, group, and other, with setuid, setgid, and sticky bit support.
Permissions
Everything runs in your browser. Nothing is uploaded.
- Owner can read and write.
- Group can read.
- Others can read.
How to calculate a chmod permission number
Toggle read, write, and execute
Check the boxes for what owner, group, and other should be able to do with the file. The octal number and symbolic string update immediately.
Or type an octal number directly
Type a value like 755 or 644 into the octal field and the permission grid updates to match it.
Add special bits if you need them
Turn on setuid, setgid, or the sticky bit to add a fourth digit to the octal number and change the symbolic string accordingly.
Copy the result
Read the plain-language description of what the permission set allows, then copy the octal number for use in a chmod command.
Why use this tool
Two-way conversion
Toggle the permission grid to build an octal number, or type an octal number to see the grid update to match it.
Special bits included
Setuid, setgid, and the sticky bit are supported and correctly change the symbolic string to s, S, t, or T where they apply.
Plain-language explanation
A short description spells out exactly what owner, group, and other can do with the current permission set, so you are never guessing.
Quick presets
Common values like 644, 755, and 4755 are one tap away for the permission sets you set most often.
Runs entirely in your browser
The calculation happens on your device; nothing about the file or the permission you are setting is uploaded.
About this tool
Unix and Linux file permissions are usually set with the chmod command, using either a three or four digit octal number like 755 or 4755, or a symbolic string like rwxr-xr-x. Both describe exactly the same thing: what the file owner, the group, and everyone else are allowed to read, write, or run. This calculator lets you build that number either way, and keeps the two views in sync as you work.
Check the boxes for owner, group, and other across read, write, and execute, and the octal number and symbolic string update instantly. Or type a number straight into the octal field and watch the grid fill in to match it. Turning on setuid, setgid, or the sticky bit adds a leading fourth digit and changes the matching letter in the execute position to s, S, t, or T, exactly as chmod and ls -l would show it.
Underneath the numbers, a short plain-language summary spells out what the current permission set actually allows, which is useful when you are handed an unfamiliar number and need to know what it means before running a command. Quick preset buttons cover the values used most often, such as 644 for a typical file or 755 for an executable or directory. Pair it with the .gitattributes generator and .gitignore generator when setting up a new repository.
Frequently asked questions
- What do the numbers in a chmod value mean?
- Each digit is a sum of read (4), write (2), and execute (1) for one group of users. The first digit is the owner, the second is the group, and the third is everyone else, so 755 means the owner gets read, write, and execute while group and other get read and execute only.
- What does a fourth digit at the front of a chmod number mean?
- A leading fourth digit sets the special bits: setuid (4), setgid (2), and sticky (1), added together the same way as the permission digits. For example, 4755 sets setuid along with the usual 755 permissions.
- What is the difference between a lowercase and uppercase s or t in the symbolic string?
- A lowercase s or t means the special bit is on and the matching execute permission is also on. An uppercase S or T means the special bit is on but execute is off for that group, which is unusual and often a sign of a misconfigured permission.
- Can I type an octal number instead of using the checkboxes?
- Yes. Type a 3 or 4 digit octal number into the octal field and the permission grid and symbolic string update to match it immediately.
- Is anything about my file uploaded when I use this calculator?
- No. The calculation is plain arithmetic that runs entirely in your browser. No file, filename, or permission value is ever sent anywhere.
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