To convert a decimal number to its octal (base-8) equivalent, we use the method of repeated division by 8. We record the remainder at each step.
Step 1: Divide 108 by 8.
$108 \div 8 = 13$ with a remainder of $4$.
Step 2: Divide the quotient (13) by 8.
$13 \div 8 = 1$ with a remainder of $5$.
Step 3: Divide the new quotient (1) by 8.
$1 \div 8 = 0$ with a remainder of $1$.
The process stops when the quotient becomes 0. The octal number is formed by reading the remainders from the bottom up.
Reading from bottom to top, we get 1, 5, 4.
Therefore, the octal equivalent of decimal 108 is $154_8$.