Chmod Calculator

Unix file permissions are compact but cryptic: the same access rights appear as 755 in a chmod command, as -rwxr-xr-x in ls -l output, and as nine checkboxes in an FTP client. This calculator translates between all three representations live: tick read, write and execute for the owner, group and others and the octal number updates instantly — or type an octal value and watch the checkboxes and symbolic string follow.

Every digit is explained rather than just displayed. The breakdown shows how each class's digit is assembled from the bit weights — read is 4, write is 2, execute is 1 — so 6 is read + write and 5 is read + execute. That is the whole system: once you see it decomposed a few times, you stop needing a calculator, which is arguably the best thing a calculator can teach you.

Below the breakdown you get a ready chmod command to copy into a terminal, and the tool warns you about risky choices: a world-writable mode or the infamous 777 triggers an explicit caution, because handing write access to every local account is the classic way web servers get compromised. Preset pages cover the modes you will actually use — 755 for directories and scripts, 644 for regular files, 600 for configs with secrets, 400 for SSH keys, and 777 with an explanation of why you usually should not.

Like every tool on this site, the calculator runs entirely in your browser: no upload, no tracking of what permissions you are setting, and it keeps working offline once loaded. It is a small, fast reference for a topic every developer, sysadmin and hosting user hits weekly.