The relative rms deviation &sgr; of the intensity of a rapidly rotating polycrystallite specimen is &sgr;=[6.5Rsin&thgr;]/[h(mNeff)½], whereR=goniometer radius, &thgr;=Bragg angle,h=(hf+hs)/2,hf=length of focal spot,hs=length of receiving slit,m=multiplicity factor, andNeffthe effective number of irradiated crystallites. Experimental data on silicon powder specimens are presented to show the dependence of &sgr; on crystallite sizes, choice of x‐ray wavelengths and various other experimental parameters. Comparisons of data for rapidly rotating and stationary specimens having crystallite sizes in the 30–50 &mgr; range show that rotation improves &sgr; by a factor of 7 or 8 for peak intensities and 4 or 5 for integrated intensities, using a standard diffractometer.