Accurate estimation of soil permeability is crucial in many geotechnical applications. Empirical and theoretical equations based on soil particle size distribution (PSD) offer a fast and cheap way for preliminary estimation of permeability in granular soils, however the results obtained from various formulas available in the literature often show significant discrepancies. While several comparative studies on this topic have been published, no definite conclusions can be drawn on the performance of the predictive equations in comparison with in-situ permeability measurements. Many formulas require porosity or void ratio as input parameter, which is difficult to obtain for granular soil in-situ. In this study we applied 30 predictive equations to estimate permeability of sandy soil in an outwash plain deposit. The equations were divided into 5 groups, based on their structure and the required input parameters. Empirical formulas were used to estimate the expected in-situ porosity range. The obtained permeability values were compared to the results of in-situ permeameter measurements and pumping tests. Significant differences in the results and in their sensitivity to porosity were found between the 5 groups of methods. In general, simple equations which do not include porosity were in better agreement with measurements than the other groups.