Octal to Decimal Converter

What is Octal to Decimal Converter?

Paste an octal (base 8) number and get its decimal equivalent instantly. Octal is used in older Unix file permission notation (like chmod 755) and some legacy systems. Conversion happens live in your browser as you type, using arbitrary-precision math, so it stays accurate even on unusually long octal strings.

Octal to Decimal Table

How to Use the Octal to Decimal Converter

1. 1

   Paste or Type an Octal Number: Enter digits 0-7 only, such as 755 or 17.

2. 2

   Read the Decimal Result Instantly: The decimal equivalent appears automatically as you type, with no button to click.

3. 3

   Copy the Result: Use the copy button to copy the decimal value for use in code or documentation.

Octal Place Values

Octal (base 8) is a positional number system where each digit represents a power of 8, just as each decimal digit represents a power of 10. The rightmost digit is the 8⁰ (ones) place, the next is 8¹ (eights), then 8² (sixty-fours), and so on. To convert, multiply each digit by its place value and add the results together.

How to Convert Octal to Decimal

Multiply each octal digit by 8 raised to its position (counting from 0 on the right), then sum the results. For example, converting octal 17: 1 × 8¹ + 7 × 8⁰ = 8 + 7 = 15 in decimal, which matches the table above. For a longer example, octal 755 (a common Unix permission value): 7 × 8² + 5 × 8¹ + 5 × 8⁰ = 448 + 40 + 5 = 493.

Octal to Decimal Examples

Octal 10 → decimal 8: 1 × 8¹ + 0 × 8⁰ = 8. Octal 12 → decimal 10: 1 × 8¹ + 2 × 8⁰ = 8 + 2 = 10. Octal 100 → decimal 64: 1 × 8² + 0 × 8¹ + 0 × 8⁰ = 64.