Octal to Decimal Converter
Enter an octal number (digits 0–7) to get its decimal value, with the powers of eight shown.
1 1110 11017554931EDWorking
7× 82 = 7 × 64 = 4485× 81 = 5 × 8 = 405× 80 = 5 × 1 = 5- Total = 493
The method
Multiply each digit by 8 raised to its position from the right (1, 8, 64, 512…) and add the products.
Place value: the idea behind every base
In any base, a digit’s worth depends on its column. Each column is worth the base times the column to its right. Tap a digit to change it and watch the total.
1×32,768 + 1×512 + 1×64 + 1×1 = 33,345 in decimal
Decimal is the same system with ten digits: 347 is 3×100 + 4×10 + 7×1. Nothing about base 10 is special apart from our ten fingers.
Octal to decimal table
| Octal | Decimal |
|---|---|
| 7 | 7 |
| 10 | 8 |
| 17 | 15 |
| 20 | 16 |
| 77 | 63 |
| 100 | 64 |
| 144 | 100 |
| 400 | 256 |
| 600 | 384 |
| 644 | 420 |
| 700 | 448 |
| 755 | 493 |
| 777 | 511 |
| 1000 | 512 |
| 7777 | 4095 |
| 10000 | 4096 |
Questions people ask
How do you convert octal to decimal?
Multiply each digit by its power of 8 and add: 755 = 7×64 + 5×8 + 5×1 = 493.
Where is octal still used?
Mainly in Unix file permissions. Each octal digit is three bits: read (4), write (2), execute (1). chmod 755 means rwx for the owner and r-x for group and others.
Why is there no 8 or 9 in octal?
Base 8 uses only the digits 0–7. After 7 comes 10, which means one eight and zero ones.