How to convert octal to decimal
- Paste octal numbers into Input, one per line. A 0o prefix or a leading 0 is fine.
- The decimal value of each line appears as you type.
- Copy the result. Any line containing 8 or 9 is flagged, since octal only uses the digits 0 to 7.
Converting octal to decimal by hand
Octal places are worth powers of 8: 1, 8, 64 and 512. Multiply each digit by its place value and add. For 755:
| Digit | 7 | 5 | 5 |
|---|---|---|---|
| Place value | 64 | 8 | 1 |
| Product | 448 | 40 | 5 |
448 + 40 + 5 = 493. The same steps turn 644 into 6 × 64 + 4 × 8 + 4 = 384 + 32 + 4 = 420. Past 7 the count carries, so octal 10 is 8, 20 is 16 and 100 is 64.
Permission digits
| Octal | Binary | Permissions |
|---|---|---|
| 0 | 000 | --- |
| 1 | 001 | --x |
| 2 | 010 | -w- |
| 3 | 011 | -wx |
| 4 | 100 | r-- |
| 5 | 101 | r-x |
| 6 | 110 | rw- |
| 7 | 111 | rwx |
A three-digit mode gives the owner, the group and everyone else one digit each, in that order. So chmod 644 means rw-r--r--, the usual mode for ordinary files, and chmod 755 means rwxr-xr-x, the usual mode for folders and programs. Single octal digits have the same value in decimal, so conversion only matters for the whole mode: 755 read as one number is 493.