Decimal to Octal Converter
Convert a decimal (base 10) number to octal (base 8) instantly. As an example, 255 = 377. It runs entirely in your browser.
| Base | This number |
|---|---|
| Binary (base 2) | — |
| Octal (base 8) | — |
| Decimal (base 10) | — |
| Hexadecimal (base 16) | — |
How to convert decimal to octal
To convert a decimal number to octal, divide it by 8 repeatedly and read the remainders from last to first. For example, 255 in octal is:
255 (decimal) = 377 (octal)
Worked example: 255 in octal
Reading 255 as base 10: 2 × 102 (= 200) + 5 × 101 (= 50) + 5 × 100 (= 5) = 255 in decimal, which is 377 in octal.
Binary, octal, decimal & hexadecimal reference table
| Decimal | Binary | Octal | Hex |
|---|---|---|---|
| 1 | 1 | 1 | 1 |
| 2 | 10 | 2 | 2 |
| 4 | 100 | 4 | 4 |
| 8 | 1000 | 10 | 8 |
| 10 | 1010 | 12 | A |
| 15 | 1111 | 17 | F |
| 16 | 10000 | 20 | 10 |
| 32 | 100000 | 40 | 20 |
| 64 | 1000000 | 100 | 40 |
| 100 | 1100100 | 144 | 64 |
| 128 | 10000000 | 200 | 80 |
| 255 | 11111111 | 377 | FF |
| 256 | 100000000 | 400 | 100 |
| 1024 | 10000000000 | 2000 | 400 |
About decimal and octal
Decimal: Decimal is base-10, the everyday number system using digits 0–9.
Octal: Octal is base-8, using digits 0–7. Each octal digit maps to exactly three bits, which is why it appears in Unix file-permission modes such as 755.
Frequently asked questions
- What is 255 decimal in octal?
- 255 in decimal (base 10) equals 377 in octal (base 8), which is 255 in decimal.
- How do I convert decimal to octal by hand?
- Repeatedly divide the decimal number by 8 and read the remainders from last to first. 255 in base 8 is 377.
- Is this exact for very large numbers?
- Yes. The converter uses big-integer (BigInt) arithmetic in your browser, so even very long decimal values convert to octal with no rounding or precision loss.
- Which characters are valid in decimal?
- Base-10 decimal uses the digits 0–9. Spaces, underscores and an optional 0x/0b/0o prefix are ignored; any other character is flagged as invalid.