Converter
Octal to Decimal Converter
Input
Output
Run process to generate output.
Frequently Asked Questions
How do I convert octal to decimal manually?
Multiply each digit by 8 raised to its positional power and sum the results. Example: octal 157 = (1×8²) + (5×8¹) + (7×8⁰) = 64 + 40 + 7 = 111 decimal.
Why does octal use only digits 0–7?
Octal is base-8, so it uses exactly 8 symbols (0–7). The digit 8 and 9 do not exist in octal. Entering 8 or 9 in an octal number is invalid — similar to how binary only uses 0 and 1.
What is the largest 3-digit octal number in decimal?
The largest 3-digit octal number is 777, which equals 7×64 + 7×8 + 7×1 = 448 + 56 + 7 = 511 decimal. This is why Unix permissions max out at 777 — 3 bits (read=4, write=2, execute=1) per permission group.