Octal to Decimal Converter
Type an octal number (digits 0–7) to get its decimal value, with each digit’s power of 8 multiplied out.
Octal uses only the digits 0–7
In decimal (base 10)
420
Octal 644 is 420 in decimal (base 10).
6×64 + 4×8 + 4 = 420
Tap a digit to step it up. Each tile is worth its digit × 8n.
Bytes in memory2 bytes, big- and little-endian
The +0, +1 … under each byte is its address offset. Big-endian puts the most significant byte first; little-endian puts it last.
How to convert octal to decimal
Octal is base 8 and uses only the digits 0 to 7. Its places are powers of 8: 1, 8, 64, 512, 4,096. Multiply each digit by its place and add.
For 755: 7 × 64 + 5 × 8 + 5 × 1 = 448 + 40 + 5 = 493. That is the decimal value behind the familiar chmod 755.
If you see an 8 or a 9, the number is not octal. Watch out for languages that treat a leading zero as octal: in C, 0755 is 493, not seven hundred and fifty-five, which is why Python 3 changed the prefix to 0o755.
value = Σ digitᵢ × 8ⁱ, with digits 0–7
- Python 3 writes octal as 0o755 and rejects a plain leading zero (0755) to avoid the C-style mix-up. Source: Python reference, integer literals.
Octal numbers in decimal
Counting to 20 in octal, where 10 means eight, then larger round octal values.
| Octal | Decimal |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 4 |
| 5 | 5 |
| 6 | 6 |
| 7 | 7 |
| 10 | 8 |
| 11 | 9 |
Show all 28 rowsShow fewer
| 12 | 10 |
| 13 | 11 |
| 14 | 12 |
| 15 | 13 |
| 16 | 14 |
| 17 | 15 |
| 20 | 16 |
| 30 | 24 |
| 77 | 63 |
| 100 | 64 |
| 144 | 100 |
| 377 | 255 |
| 400 | 256 |
| 755 | 493 |
| 777 | 511 |
| 1000 | 512 |
| 1750 | 1,000 |
| 7777 | 4,095 |
Frequently Asked Questions
What is 10 in octal as a decimal?
Octal 10 is 8: one eight and no ones. Octal counts 0, 1 … 7 and then 10, the same way decimal goes from 9 to 10.
What does chmod 644 mean in decimal?
Octal 644 is 6 × 64 + 4 × 8 + 4 = 420. The decimal value rarely matters for permissions: each octal digit is read on its own as three permission bits (6 = rw-, 4 = r--).
Where is octal still used?
Mostly Unix file permissions and some older systems with 12, 24 or 36-bit words. Hex replaced it for most work once 8-bit bytes became standard, because two hex digits fit a byte exactly.