Several methods for determining the hydraulic conductivity-volumetric water content relationship have been developed. We evaluated on a sand dune soil three different methods for determining hydraulic conductivity values. The first method is known as the internal drainage-instantaneous profile method and was carried out on the field. The second method was analogous to the first but was carried out in the laboratory. The results obtained by these two experimental techniques were then used as a reference for comparing with the hydraulic conductivity functions predicted by the third method, mathematical models. For this numerical approach, the Jackson and the Mualem formulation was selected. For the coarse-textured soil used in this investigation, all three methods resulted in hydraulic conductivity functions that were in fairly good agreement. Moreover, the differences between the laboratory experiment and the field experiment were greater than the deviations of the mathematical models, although subtle differences were found. It seemed that Mualem's model for calculating the hydraulic conductivity function, combined with the van Genuchten equation for the soil water retention equation, is the easiest to use and leads to the most accurate results for this particular soil.