To calculate the interior angle of a regular polygon, we use the formula:

\(\text{Interior Angle} = \frac{(n - 2) \times 180^\circ}{n}\)

where \( n \) is the number of sides. For a 5-sided polygon (pentagon):

\(\text{Interior Angle} = \frac{(5 - 2) \times 180^\circ}{5} = \frac{3 \times 180^\circ}{5} = \frac{540^\circ}{5} = 108^\circ\)

Thus, the interior angle of a regular pentagon is \( 108^\circ \).