This International Standard describes procedures for measuring average grain size derived from a two-dimensional polished cross-section using electron backscatter diffraction (EBSD). This requires the measurement of orientation, misorientation and pattern quality factor as a function of position in the crystalline specimen[1].NOTE 1 While conventional methods for grain size determination using optical microscopy are well-established, EBSD methods offer a number of advantages over these techniques, including increased spatial resolution and quantitative description of the orientation of the grains.NOTE 2 The method also lends itself to the measurement of the grain size of complex materials, for example those with a signifcant duplex content.NOTE 3 The reader is warned to interpret the results with care when attempting to investigate specimens with high levels of deformation.