chmod Permission Calculator

Calculate Unix file permissions using checkboxes and see the numeric chmod value with command preview.

Tested tool guide Tested browser tools Checked August 16, 2026

What chmod Permission Calculator does, with a checked example

chmod Permission Calculator maps the nine ordinary Unix permission choices - read, write, and execute for owner, group, and others - to a numeric chmod value and a command preview. Select the checkboxes that describe the access you want, then copy the resulting mode or command. The common mistake is totaling all selected permissions together. Each subject class gets its own digit, so owner read and write becomes 6 while group read and others read each become 4, producing 644.

Worked example

A concrete input and expected output from the current implementation.

Input

Owner: read and write; Group: read; Others: read

Expected output

Owner read and write is 4 + 2 = 6. Group read is 4, and others read is 4, so the three digits are 644.

How the result is produced

Calculate each digit

For each class, the calculator assigns read a value of 4, write a value of 2, and execute a value of 1. It adds only the checked values within that class. A class with read and execute selected totals 5; with no boxes selected, it totals 0. Every ordinary permission digit is therefore between 0 and 7.

Order the classes

The class totals are ordered owner first, group second, and others third. Those digits form the numeric mode shown by the calculator. Its command preview places that mode after chmod so the result can be copied into a shell command with the intended path. The preview does not inspect or change any file.

Good uses

Convert a desired owner, group, and others access pattern into a three-digit mode before running chmod.
Check whether a mode such as 640 actually represents the read and write permissions you intend.
Prepare a chmod command when deployment instructions describe permissions in words instead of numeric notation.

Limits and checks

The calculated mode describes permission bits, but it does not show the target file's ownership, access control lists, or other filesystem restrictions.
Execute has different practical meaning for files and directories. On a directory, it controls searching and traversal rather than running the directory.
The command preview is text only. Running it still requires the correct path and sufficient permission to change that target.

Common questions

Why does read plus write produce 6?

Within one permission class, chmod represents read with 4, write with 2, and execute with 1. Selecting read and write therefore gives 4 + 2 = 6. The same calculation is performed separately for owner, group, and others, which is why a result normally contains three permission digits.

Does 755 mean the same thing for a file and a directory?

It sets the same bit pattern: owner gets read, write, and execute, while group and others get read and execute. The effect is not identical. Execute can permit a file to be run, subject to other system conditions. For a directory, execute permits traversal and access to entries whose names are known.

References and verification

The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.