A method for the determination of the intensity of the solar light scattered by a unit volume of interplanetary space and thus the density and phase functions of interplanetary dust is presented. The method involves the calculation of the scattered light intensity as a function of sun-particle distance and elongation angle from a partly assumed, partly observed brightness in the symmetry plane of the cloud. The scattered light intensity at a given sun-particle distance can then be decomposed to obtain expressions for the particle density and phase function. Ground-based and Pioneer X determinations of the density as a function of distance and the phase function of elongation are then obtained without the use of previous assumptions.