A computer based method for the calculation of dispersion force distributions of irregular shaped particles is presented in this paper. To accomplish this the particles are brought in contact with a wall surface and rotated randomly into a large number of orientations to the surface normal, equally distributed in respect to the possible orientations. Then in each case the London-van der Waals dispersion force is calculated, holding the surface-surface distance on a constant value, which finally results into a force distribution. This distribution gives information about the possible dispersion forces attributed to a certain particle shape and size in the case particle-slab. Using the Hamaker summation method in parts, the computing effort raises with growing particle sizes. So a method has been developed to reduce the problem to 2D, from which it is possible to reconstruct the 3D force distribution.