chmod Calculator
Tick permissions and get the chmod number โ 755, 644 and friends explained.
About this calculator
Tick permissions for owner, group and others and read off the octal (755) and symbolic (rwxr-xr-x) forms โ or type a number and watch the boxes follow. The command line updates live and copies in a click, and the common presets are one tap away. It also warns you before you 777 something.
How the numbers work
Each digit is a sum: read = 4, write = 2, execute = 1. So 7 is everything (4+2+1), 6 is read+write, 5 is read+execute, 0 is nothing โ and the three digits apply to the file's owner, its group, and everyone else, in that order. The vocabulary you'll use forever: 644 for ordinary files (owner edits, world reads), 755 for scripts and directories (as 644, plus execute), 700 / 600 for private things like SSH keys, and 777 almost never โ world-writable files on a shared server are an invitation. For directories, execute means "can enter", which is why folders need 755 where files need 644.
Frequently asked questions
What does chmod 755 mean?
rwxr-xr-x โ the owner can read, write and execute; group and others can read and execute but not modify. The standard mode for scripts, binaries and directories.
What's the difference between 644 and 755?
The execute bit. 644 (rw-r--r--) suits ordinary files; 755 adds execute for scripts โ and for directories, where execute means permission to enter.
Why is chmod 777 a bad idea?
It lets every user on the system modify the file. On shared hosting that's how sites get defaced; the right fix for a permission error is almost always correct ownership plus 755/644, not 777.
What does execute mean on a directory?
Permission to enter it and reach the files inside. A directory with read but not execute lets you list names but open nothing โ which is why directories generally need the execute bits set.