Quantitatively linking observations from independent non-invasive soil assessment methods enhances our ability to understand root zone processes. Electrical Resistivity Tomography (ERT) and X-ray Computed Tomography (CT) are two advanced non-invasive technologies routinely employed in soil science. ERT allows 4D process monitoring (e.g., solute transport) and is sensitive to changes in moisture content (MC) and soil texture. X-ray CT is a higher resolution method used to appraise soil structure. We measured the variation of electrical resistivity and X-ray absorption with gravimetric moisture content (GMC) for two distinct soil types. Experimental results were compared with existing pedophysical relationships that express these dependencies. Based on the good fit between measurements and model predictions, we formulated a new pedophysical relationship that links directly the two soil properties. This will allow a direct translation between ERT and X-ray data for the study of root-zone parameters under well-defined experimental circumstances.