A scaling technique is presented for estimating the hydraulic conductivity based on experiments of horizontal infiltration of water into an air-dry soil. From plots of the distance from the water source to the wetting front as a function of the square root of time, a scaling factor is obtained that permits the estimation of the hydraulic conductivity as a function of soil water content.The method has been established experimentally using five Brazilian tropical soils and seven California temperate soils, with one of them being taken as a standard soil. Bulk density measurements used to verify the homogeneity of each soil column and volumetric soil water content measurements were made by gamma-attenuation using137Cs.