In deriving particle size, volume and concentration from laser diffraction experiments, it is normally assumed that the particles are spheres. For other shapes the projected area is not constant but rather has a range of values. Because the orientation of the body is usually random, it is the distribution function for the projected area which is of interest. In order to assist in the interpretation of light diffraction measurements and image analysis, the distribution of the projected area for (tri-axial) ellipsoids and general cylinders is derived. The graph of the distribution is given for an ellipsoid with axes in the ratio 1:2:8. The distribution function for a general cylinder, given in terms of the width function of its base, is expressed in a form suitable for numerical computation. Examples are given and also analytic results for the circular cylinder and cube.