The distribution functions of grain sizes are determined for engineering sheet materials of 6-4 brass, copper, SS-41 and aluminum with a sufficient accuracy. Statistical variables of a mode, a median and a standard deviation are determined in addition to a mean. Flow stress is found not necessarily to obey the Hall-Petch relationship in all ranges of plastic strain and the mean grain size employed here except the results in 6-4 brass. The strain hardening exponent (n) increases in a parabolic way as the mean grain diameter increases. The dependence of strength and ductility on the strain rate is shown and the n-value increases as the strain rate increases in SS-41. Variation of the n-value with respect to the width to thickness ratio of a specimen is also discussed for copper.