Decimal to Octal:
\[ \begin{array}{c} \text{Divide the decimal number by 8 repeatedly until the quotient is zero} \\ \text{Collect the remainders from each division} \\ \text{The octal number is the remainders read from bottom to top} \end{array} \]
Octal to Decimal:
\[ \text{Decimal} = \sum_{i=0}^{n} \text{Digit}_{i} \times 8^{i} \]