Decimal ↔ Octal Converter
Free online decimal to octal and octal to decimal converter. Convert between base-10 and base-8 instantly.
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Tip: Type in either field. Octal uses digits 0-7 only.
💡 Definition
Octal Number System
- Octal (base-8) uses digits 0 through 7.
- Each octal digit represents exactly 3 binary bits.
- Octal was historically important in early computing and is still used for Unix/Linux file permissions (e.g., chmod 755).
📖 How to use
Step by Step
- Enter a decimal number on the left
- The octal equivalent appears on the right
- Or enter an octal value to get decimal
- Only digits 0-7 are valid in octal
🎯 Use cases
When to use
- Unix/Linux file permissions (chmod)
- Legacy computing systems
- Digital electronics grouping (3-bit)
- PDP-8 and other historical architectures
Frequently Asked Questions
What is octal used for today?▾
The most common modern use is Unix/Linux file permissions. For example, chmod 755 sets rwxr-xr-x. Each digit (7, 5, 5) represents a 3-bit binary value for owner, group, and others.
What does 0o mean in programming?▾
The "0o" prefix in Python and JavaScript indicates an octal literal. For example, 0o377 = 255 in decimal. C uses a leading 0 (e.g., 0377).