A theoretical discussion of the ratio between apparent resistivity and real resistivity of a soil layer as a function of (i) layer thickness/electrode spacing ratio; (ii) the soil layer thickness and resistivity of an underlying layer; and (iii) horizontal distance of a different medium from the current electrode is presented. Laboratory experimental work was carried out in order to study the effects the electrode spacing and current density have on the determination of the electrical conductivity of soil solution. It was found out that the depth sensed by a Wenner Configuration would be deeper than the inner electrode spacing for most field situations and especially where there are large variations in conductivity (due to salinity or water content) with depth. The laboratory calibration of the salinity probe should be done in a volume of about 2.5 liters or greater. The volume sensed by this method is greater the lower is the water content. The implications in laboratory calibration‐field measurements relationships are discussed.