Convert Decimal to Octal

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

Selected Decimal (dec) - available characters: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Conversion Formula

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

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

Step 1: Input is already decimal - skip to Step 2.
        Value: 42

Step 2: Divide 42 by 8 repeatedly (read remainders upward):

        42 ÷ 8 = 5  r 2
         5 ÷ 8 = 0  r 5
        Read remainders upward: 52

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

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.

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.

Quick Reference Table

→ Full Number Base Converter