Chmod Calculator for Unix & Linux File Permissions
The Chmod Calculator turns Unix and Linux file permissions into octal numbers, symbolic notation, and ready-to-run chmod commands using an interactive permission matrix. Click the read, write, and execute boxes for owner, group, and others, and every format updates at once. It is built for developers, sysadmins, and anyone who would rather not memorize octal codes.
You can work from any direction: tick the boxes, type an octal value like 755, or paste symbolic notation like rwxr-xr-x — the calculator keeps the matrix, the inputs, and the generated commands in sync. Special permissions (setuid, setgid, sticky bit), a file or directory toggle, and a recursive flag are all built in, so the command you copy is exactly the one you need in the terminal.
How to Use the Chmod Calculator
Set permissions in the matrix
Tick Read, Write, and Execute for Owner, Group, and Others. Each role's octal total (4 + 2 + 1) updates as you click.
Or type octal / symbolic directly
Enter a 3-digit octal value like 644 (or a 4-digit value like 4755 with special bits), or type symbolic notation like rwxr-xr-x. The matrix and the other field sync automatically.
Tune options and presets
Pick a preset (644, 755, 777, 700, 600, 400, 775, 000), toggle Special bits, switch the File / Directory type, or enable Recursive to add -R to the command.
Copy the chmod command
The output shows ready-to-use octal and symbolic chmod commands plus an ls -l preview. Click Copy next to a command and paste it into your terminal.
Features
Interactive Permission Matrix
A 3x3 grid toggles Read (4), Write (2), and Execute (1) for Owner, Group, and Others, with the per-role octal total updating live.
Bidirectional Sync
Edit the matrix, type octal, or paste symbolic notation — every field updates in real time with no Calculate button.
Common Presets
One-click values for 644, 755, 777, 700, 600, 400, 775, and 000, each with a tooltip explaining its typical use.
Special Permissions
Toggle Setuid (4), Setgid (2), and Sticky Bit (1) to build 4-digit octal values; symbolic notation shows s/S and t/T correctly.
File / Directory Preview
Switch between File and Directory to see how permissions render in ls -l output, with a - or d prefix.
Recursive Flag
Enable Recursive to add -R to the generated chmod commands when applying permissions to a directory tree.
Ready-to-Run Commands
Generates both octal and symbolic chmod commands with one-click copy buttons, ready to paste into your shell.
Octal Breakdown
Shows how each role's value is summed — for example, read + write + execute as 4 + 2 + 1 = 7 — so the math is never a mystery.
Frequently Asked Questions
What does chmod 755 mean?
755 (rwxr-xr-x) gives the owner full read, write, and execute, while group and others get read and execute only. It is the standard choice for directories and executable files. Permission 644 (rw-r--r--) drops execute and is the usual setting for regular files.
How do read, write, and execute map to 4, 2, and 1?
Each permission has a numeric weight: read = 4, write = 2, and execute = 1. Add the weights you want for a role to get its octal digit — read + execute is 4 + 1 = 5, and read + write + execute is 4 + 2 + 1 = 7. Repeat for owner, group, and others to build the full value, exactly as the calculator's breakdown shows.
What is the difference between 755 and 777?
755 lets only the owner write, while group and others can read and execute. 777 grants read, write, and execute to everyone, including group and others. 777 is generally not recommended for production because anyone can modify the file; reserve it for temporary testing or specific shared directories where every user truly needs full access.
What is the difference between symbolic and octal notation?
Octal uses numbers such as 755, where each digit is the sum of permissions (4 = read, 2 = write, 1 = execute). Symbolic uses letters such as rwxr-xr-x, where r = read, w = write, x = execute, and - means the permission is off. Both describe the same access; the calculator converts between them instantly.
What are setuid, setgid, and the sticky bit?
Setuid (4) runs an executable with the permissions of its owner. Setgid (2) makes new files in a directory inherit that directory's group. The Sticky Bit (1) stops users from deleting files they do not own in a shared directory — commonly used on /tmp. Toggle any of these to produce a 4-digit octal value.
How do I apply permissions recursively?
Enable the Recursive option to generate a command like chmod -R 755 filename. The -R flag applies the same permissions to a directory and every file and subdirectory inside it. Use it carefully on large trees, since it changes everything beneath the target.
What permission should I use for SSH keys?
An SSH private key should use 600 (rw-------) so only the owner can read and write it; SSH refuses keys with broader permissions. The .ssh directory itself should be 700. Both are available as one-click presets in the calculator.
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