Convert Octal to Decimal

Convert Octal (oct) to Decimal (dec) instantly and accurately.

Selected Octal (oct) - available characters: 0, 1, 2, 3, 4, 5, 6, 7

Conversion Formula

Step-by-step example using the value 42 (decimal):

Convert Octal (base 8) → Decimal (base 10)

Step 1: Expand each digit of 52 (oct) by position:

        5 × 8^1 = 40
        2 × 8^0 =  2
        ────────────
        Sum = 42 (decimal)

Step 2: Target is decimal - Step 1 result is the final answer.

────────────────────────────
Result:  52 (oct) = 42 (dec)

About Octal

Octal (base 8) uses digits 0-7. Each position is a power of 8: 8⁰=1, 8¹=8, 8²=64. Because 8 = 2³, each octal digit = exactly 3 binary bits. The Unix/Linux file permission system (chmod 755 = rwxr-xr-x; 7=111, 5=101) uses octal for concise 3-bit rwx triplets. The DEC PDP series encoded 12- and 16-bit words naturally in octal. In C/C++/JS a leading zero denotes octal: 0755 = 493₁₀. Conversion: decimal 42 = 5×8+2 = 52₈.

About Decimal

Decimal (base 10) is the universal positional system using digits 0-9. Each position is a power of 10: 10⁰=1, 10¹=10, 10²=100. Attributed to human anatomy (ten fingers). The Hindu-Arabic system - including zero - was formalised by Brahmagupta (628 CE) and spread via al-Khwarizmi (c. 820 CE). SI and metric systems are base-10. IEEE 754-2008 added decimal64/128 formats for exact decimal arithmetic in financial applications. Conversion: decimal 42 is the reference value used throughout this converter.

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