Simple two-parameter models were proposed for correlating grain size to process conditions and phase diagram variables. However, these models have not been fully examined using data obtained from well controlled experiments. This work intended to clarify these models with selected experimental data obtained in dilute hypoeutectic alloys. Criteria for data selected were proposed. The selected experimental data were fitted by these models to examine curve fitting quality and the applicability. Models that fit experimental data better were identified. Mechanisms by which grain size is reduced under the influence of a solute element were examined based on the data analysis. Results suggest that there is a clear dependence of grain size on the solidification interval of an alloy, which can be expressed as the P variable. Such a clear dependence of grain size on solidification interval indicates that mechanisms that are associated with dendrite fragmentation are the dominant operating mechanisms governing grain refinement by solute element in ingots and castings where convection in the molten alloy exists during its mold filling and solidification.