Octal Calculator – Base 8 Arithmetic and Conversion
Convert and calculate with octal (base 8) numbers.
About This Calculator
Convert and calculate with octal (base 8) numbers. Use the calculator above for instant results.
Worked Examples
- 15 + 5 = 20 decimal | Octal: 24
Answer: 0o24 (20 decimal)
- Octal 755 = 493 decimal | rwxr-xr-x
Answer: 493 decimal / rwxr-xr-x
- 15 × 3 = 45 decimal | Octal: 55
Answer: 0o55 (45 decimal)
Who Uses This Calculator?
Unix file permissions use octal (chmod 755).
Number base conversion practice.
Demo octal arithmetic.
Some legacy systems use octal.
Common Mistakes to Avoid
❌ 8 and 9 are not valid octal
Octal uses only digits 0-7. Using 8 or 9 is an error.
❌ Octal confusion in C
In C, a leading 0 makes a literal octal: 010 = 8, not 10! This causes bugs in date/time formatting code.
Frequently Asked Questions
Octal today?
Primarily used for Unix file permissions (chmod 644, 755, 777). Legacy use in older systems.
Unix permissions in octal?
3 digits: owner/group/others. Each: 4=read, 2=write, 1=execute. 755 = rwxr-xr-x. 644 = rw-r--r--.
Octal vs hex?
Both are power-of-2 bases useful for binary representation. Hex (16) = 4 bits per digit. Octal (8) = 3 bits per digit. Hex is now more common.