Soil thermal conductivity is an important physical property which is related to the volume fractions of solid-liquid-gas. In the solid phase, the distribution of particles plays an important role as well as their spatial arrangement. In this work two different materials have been used to calibrate thermal conductivity measurements applying a recent laboratory method established by Zuñiga (2002). This method consists in an electro-thermal probe that at a certain intensity and potential the electricity is transformed in heat energy that gradually increases the sample temperature. The temperature variation is plotted versus time in natural logarithm scale. The slope of the curve obtained gives an estimation of the thermal conductivity of the studied material. There are two methods to estimate this slope based on a linear approach after a certain heating time or a polynomial approach for the whole curve. A comparison of both methods based on the results obtained with two standardized materials, clayey and sand, is presented.