If you're using a Pro version, use AddOns>Special Tools>Analyze>2D Geometric Parameters. First use the Section tool to create the cross section. This produces a "Group" which must be exploded one time. After exploding, select the Polyline that defines the outline of the section, move it aside, and delete the rest. Since the analysis tool reports results with respect to the World coordinate system, you'll probably want to place the polyline on the World workplane and move it to the World coordinate system origin.