An interior angle of a polygon is an angle inside a polygon at a vertex of the polygon.

Interior angles of a regular polygon are equal in measure. The magnitude of an angle can be determined by the number of sides of the polygon.

When the measure of one interior angle of a regular polygon is determined, it can be multiplied by the number of sides of the polygon to find the sum of the interior angles of the polygon.

The following are "formulas" to determine the measure of an interior angle of any n-sided regular polygon and to determine the sum of the measures of all interior angles of a regular polygon.