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Octal to Decimal Converter - Free Online Octal Calculator

Free online octal to decimal converter and calculator. Convert octal to decimal, decimal to octal, with hex and binary output. Reference table included. No signup required.

OctalDecimalBinary
000
77111
1081000
17151111
7763111111
100641000000
1771271111111
37725511111111
777511111111111
10005121000000000
77774095111111111111
177777655351111111111111111

Octal to Decimal Converter Online

This octal to decimal converter tool allows you to easily convert between octal (base-8) and decimal (base-10) number systems. Enter an octal value to see its decimal, hexadecimal, and binary equivalents instantly. The tool supports bidirectional conversion and includes a reference table of common octal values. Useful for Unix file permissions, programming, and computer science. All processing happens in your browser โ€” your data never leaves your device.

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FAQ

What is the octal number system?
Octal (base-8) uses digits 0-7. Each octal digit represents exactly 3 binary bits. It was historically important in computing and is still used in Unix file permissions (chmod 755), some programming languages (0o777), and legacy systems.
How do I convert octal to decimal?
Multiply each digit by its positional power of 8. For example, 755 in octal = 7*64 + 5*8 + 5*1 = 448 + 40 + 5 = 493 in decimal. The tool does this calculation instantly.
Where is octal used in programming?
Primarily in Unix/Linux file permissions (chmod 755 = rwxr-xr-x), some C/C++ literals (0755), Python (0o755), and legacy mainframe systems. Octal was more common when computer word sizes were multiples of 3 bits.
What is chmod 755 in decimal?
chmod 755 in octal equals 493 in decimal. Each digit represents permissions for owner (7=rwx), group (5=r-x), and others (5=r-x). The octal notation maps directly to the 3-bit permission groups (read=4, write=2, execute=1).