Approximate value of solid angle subtended by an elliptical plane at any point lying on the axis passing through the centre can be calculated by using HCR's Approximation Formula which is applicable on any plane having at least two axes of symmetry & factor of circularity closer to unity for a given location of the observer in the space. It is equally applicable for rectangle, square, rhombus, ellipse, circle & all other symmetrical planes having at least two axes of symmetry.