Decimal to octal — base-10 to base-8
Enter a whole number and this tool returns its octal (base 8) value, plus the binary and hexadecimal forms. Octal is most familiar from Unix file permissions (modes like 755 and 644) and from older computing systems where bits are grouped in threes.
How it works
Octal is base 8, using only the digits 0-7. Each octal digit represents exactly three binary bits, since 2³ = 8. To convert, the number is repeatedly divided by 8 and the remainders are read in reverse order. In the Unix permission context, each digit is the sum of read (4), write (2) and execute (1) for a class of user. The tool also derives the binary and hexadecimal equivalents. Inputs must be whole, non-negative integers up to 9,007,199,254,740,991.
Example
Convert 420:
420 ÷ 8 = 52 r 4; 52 ÷ 8 = 6 r 4; 6 ÷ 8 = 0 r 6 → read upward → 644
As a file mode, 644 means owner read/write, group read, others read.
| Base | Value |
|---|---|
| Decimal (10) | 420 |
| Octal (8) | 644 |
| Binary (2) | 110100100 |
| Hex (16) | 1A4 |
The conversion runs entirely in your browser — nothing is uploaded.