Chmod Calculator — Octal ↔ rwxr-xr-x Permissions
Convert chmod octal modes (755, 644) to symbolic rwx notation and back — see exactly what owner, group and others can do, plus what each common preset is for.
Last reviewed 2026-10-19. Rates change — verify against the official sources linked below before relying on these figures.
What this is based on
- Covers the standard permission bits (rwx per owner/group/other) plus the setuid/setgid/sticky digit when a 4-digit octal is given.
- The 'x' bit means execute for files and traverse (enter) for directories — same letter, different meaning.
- Symbolic input expects the full 9 characters including dashes (rw-r-----).
- Everything runs locally in your browser — pasted content is never uploaded, logged or stored.
Octal is just binary triplets
Each digit is a 3-bit permission set: read=4, write=2, execute=1, added together. 7=rwx (4+2+1), 6=rw-, 5=r-x, 4=r--, 0=---. Three digits = owner, group, others in that order — so 755 is 'owner everything, everyone else read+enter'.
A leading fourth digit carries special bits: 4=setuid, 2=setgid, 1=sticky. 1777 is the sticky world-writable /tmp setup; 4755 makes a file run as its owner.
The presets you'll actually use
644 for regular files (you write, everyone reads). 755 for executables and directories. 600 or 400 for secrets — SSH refuses keys that are group/other readable. 700 for private directories like ~/.ssh.
777 is almost never right: world-writable files are the classic shared-hosting foothold. If 'only 777 works', the real fix is ownership (chown), not wider permissions.
Frequently asked questions
- What does chmod 755 mean?
- Owner: read+write+execute (7=rwx); group and others: read+execute (5=r-x). Standard for scripts and directories.
- What does 644 allow?
- rw-r--r-- — owner can write, everyone can read. The default for web-served files and source code.
- Why does SSH complain about my key permissions?
- SSH requires private keys to be owner-only: chmod 600 id_rsa (or 400). Anything group/other readable is rejected as insecure.
- What does the x bit do on a directory?
- Traverse — you can cd into it and reach files inside. Without x, even knowing a file's exact path won't let you open it.
Related calculators
Convert between decimal, hexadecimal, binary and octal instantly — accepts 0x, 0b, 0o prefixes, handles huge numbers exactly (BigInt, no float overflow).
Paste a Dockerfile and get an instant security review: baked secrets, unpinned base images, root containers, curl-pipe-to-shell and remote ADD — all checked locally.
Paste HTTP response headers and instantly see which security headers are missing — HSTS, CSP, X-Frame-Options, nosniff, Referrer-Policy, Permissions-Policy — plus cookie flag and Server version checks.