Octal to Decimal Converter Online
Convert between octal and decimal number systems instantly in your browser. This free tool runs entirely client-side — no data is sent to any server.
Number Base Converter
Convert numbers between binary, octal, decimal, and hexadecimal. Results update as you type.
About Number Base Conversion
- Supports arbitrarily large numbers using BigInt — no precision loss.
- Use prefixes for quick input:
0bfor binary,0ofor octal,0xfor hex. - Underscores in input are ignored for readability (e.g.
1_000_000). - Everything runs in your browser — no data is sent over the network.
What is octal to decimal conversion?
Octal (base-8) uses digits 0-7 and was historically popular in computing because it groups binary digits into sets of three. Converting octal to decimal multiplies each digit by 8 raised to its position power. For example, octal 755 equals (7×64) + (5×8) + (5×1) = 493 in decimal.
Common use cases for octal-decimal conversion
Octal is most commonly encountered in Unix/Linux file permissions (chmod values like 755, 644, and 777). It is also used in some programming languages as a number literal prefix (0o755 in Python, 0755 in C). Understanding octal to decimal conversion is important for correctly setting and interpreting file permissions on Linux servers.
Frequently Asked Questions
What do octal file permissions like 755 mean?
In Unix permissions, each octal digit represents read (4), write (2), and execute (1) permissions. 755 means the owner has full access (7=4+2+1), while the group and others have read and execute access (5=4+1). The decimal equivalent is 493.
Why is octal used for file permissions instead of decimal?
Octal maps perfectly to 3-bit permission groups (rwx). Each octal digit 0-7 represents exactly three binary bits, making it easy to read permission combinations at a glance. Decimal does not have this convenient alignment.