Grain size in a single-phase film such as polycrystalline silicon can be a difficult quantity to measure because grains are differentiated from one another by crystallographic orientation alone. This paper describes a simple method for determining average grain size in polycrystalline silicon using transmission electron microscope (TEM) convergent beam electron diffraction (CBED) patterns to delineate grain boundaries. Measurements are compared with results obtained using bright-field TEM contrast and surface topography as measured by atomic force microscopy (AFM). Results show a reasonable agreement between the techniques; in particular, CBED and AFM measurements are close enough that a correlation may be made.