A simple experimental method for determining the efficiency of second harmonic generation (SHG) using small amounts of dry crystalline powder is described. Contrary to previous techniques, the light scattering effects are explicitly accounted for, and a procedure to eliminate their influence is proposed. The method also permits to assess whether a particular crystal is phase matchable or not. Second-order susceptibility coefficients of eight relevant materials for SHG are determined, and the agreement with the single-crystal data is, in general, fairly good. For polycrystalline ZnSe samples, a situation of the so-called random quasiphase matching is evidenced.