Composite areas comprise multiple basic shapes, such as rectangles, triangles, and circles, connected in some way. Calculating the second moment of area for a composite shape involves subdividing it into basic shape components. The centroid for each component is calculated, from which the centroid for the composite can be obtained. Next, the second moment of area for each component about a reference axis is calculated using the parallel axes theorem. Finally, the summation of moments for each section gives the moment of inertia for the composite area. For example, an L-shaped beam comprises two perpendicular rectangles. The centroid for each rectangular section is used to calculate the centroid for the beam. The second moments of area for the rectangles about the respective centroidal axes are known. The distance from each rectangle's centroid to the beam's centroid is substituted in the parallel axis theorem to estimate its second moment of area about the reference axis. The summation of the moments for both rectangles gives the second moment of area for the beam about the reference axis.