This part of ISO 4499 gives guidelines for the measurement of hardmetal grain size by metallographic techniques only using optical or electron microscopy. It is intended for sintered WC/Co hardmetals (also called cemented carbides or cermets) containing primarily WC as the hard phase. It is also intended for measuring the grain size and distribution by the linear-intercept technique. This part of ISO 4499 essentially covers four main topics: - calibration of microscopes, to underpin the accuracy of measurements; - linear analysis techniques, to acquire sufficient statistically meaningful data; - analysis methods, to calculate representative average values; - reporting, to comply with modern quality requirements. The part of ISO 4499 is supported by a measurement case study to illustrate the recommended techniques (see Annex A). The part of ISO 4499 is not intended for the following. - Measurements of size distribution. - Recommendations on shape measurements. Further research is needed before recommendations for shape measurement can be given. Measurements of coercivity are sometimes used for grain-size measurement, but this current guide is concerned only with a metallographic measurement method. It is also written for sintered hardmetals and not for characterising powders. However, the method could, in principle, be used for measuring the average size of powders that are suitably mounted and sectioned.