Decimal to Octal Converter — Free Online Base 10 to Base 8
Convert decimal (base 10) numbers to octal (base 8) instantly — essential for Unix chmod file permissions.
Tip: Enter multiple values (one per line) for batch conversion.
Frequently Asked Questions
Decimal to Octal Conversion and Linux Permissions
The most practical use of decimal-to-octal conversion in modern computing is calculating Unix file permissions. When you run chmod 755 script.sh, you're using octal. The 3-bit structure of Unix permissions (read=4, write=2, execute=1 per group) maps exactly to one octal digit per permission group.
To convert: divide by 8 repeatedly, collect remainders. For permission value 493 in decimal: 493 = 7×64 + 5×8 + 5 = octal 755. In code, use number.toString(8). Most developers type the octal value directly rather than computing it, but this tool is useful when you know the decimal representation of a permission mask.
Beyond file permissions, octal appears in C source code (literals prefixed with 0), some network protocol specifications, and embedded systems programming where 3-bit groupings are natural. It was more common on early DEC minicomputers (PDP-8, PDP-11) whose word sizes were multiples of 3 bits.