Henry: Thank you for the insight. Regarding the case in point, a torus (a circle revolved). I wanted to get a handle on what the TC Area of Inertia was and how to use it for two types of torus, a solid and a membrane, in each case I know the mass, the surface area, and the volume. Then progress into irregular revolved 'solid' shapes of which I also would know the mass, SA, Vol. Perhaps the TC area of inertia, (as you indicated, is the integral of x^2*dA), is meant only for a surface, not a volume. As seen in my spreadsheet example it did provide the correct answer when used for a surface (membrane configuration), and correlated exactly with the answer provided by your equation: mass*(R^2+1.5r^2). I think I'll just have to play around with different examples to feel more comfortable with it, and understanding of it and its use for solids. For an irregular shape, perhaps the key lies in obtaining a 'radius of gyration' from the 2D shape. Appreciate your erudite contributions to my learning process. Really! Thanks again. Roger