Octal to Decimal

Convert octal numbers to decimal. Essential for Unix/Linux system administrators working with file permissions and legacy computing systems.

What is the Octal to Decimal Converter?

This tool converts octal numbers (base-8) to decimal numbers (base-10), useful for system administration and legacy computing.

How it works: each octal digit represents a power of 8. Reading right to left, the place values are 1, 8, 64, 512, and so on.

Why Convert Octal to Decimal?

Unix/Linux Permissions

chmod 755 maps to specific access levels for each user class.

Legacy Systems

Older computers commonly used octal notation.

Programming

Some languages support octal literals such as 0o755.

Digital Systems

Octal groups binary into convenient 3-bit chunks.

The Conversion Method

Multiply each octal digit by its place value (a power of 8) and add the results together.

Example: 755 = 7×64 + 5×8 + 5×1 = 448 + 40 + 5 = 493.

How to Use

Enter the Octal Number

Use the digits 0–7 only.

View the Decimal Result

The conversion is automatic and appears as you type.

Understand the Value

Copy the decimal result — useful for permission calculations and comparisons.

Bidirectional: both fields are editable. Type a decimal value in the result field to convert it back to octal, or use the swap button to flip the direction.

Unix Permission Examples

Octal	Decimal	Permission
644	420	rw-r--r--
755	493	rwxr-xr-x
777	511	rwxrwxrwx
400	256	r--------

Frequently Asked Questions

Are 8 and 9 valid in octal?

No. Octal uses only the digits 0 through 7. The digits 8 and 9 are not part of the system and will be rejected.

Why is 755 equal to 493?

755 in octal is 7×64 + 5×8 + 5×1 = 448 + 40 + 5 = 493. This is why chmod 755 corresponds to the decimal value 493.

What does rwx = 421 mean?

Each permission has a value: read = 4, write = 2, execute = 1. Adding them gives the octal digit for that user class, so rwx = 4 + 2 + 1 = 7.

How do I convert decimal back to octal?

Type a decimal number directly into the result field, or press the swap button to reverse the conversion direction.

Octal OCT 01234567

Decimal DEC 0123456789

Common Conversions

7 = 7

10 = 8

77 = 63

100 = 64

755 = 493

777 = 511

Octal (Base-8)

Uses digits 0-7. Historically important in computing. Still used for Unix file permissions (rwx = 421).

Decimal (Base-10)

Standard number system for everyday use and calculations.

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