This paper introduces dimensional analysis in Non-Destructive Testing & Evaluation (NDT&E) problems. This is the first time that this approach is adopted in the framework of NDT&E, and the paper opens to the development of probes and methods to simultaneously estimate several parameters with a simple approach. The most important theorem of dimensional analysis is the Buckingham's π theorem, based on the concept that the laws of the physics do not depend on the particular set of units chosen. The core of this theorem is a systematic reduction in the number of variables describing a physical problem. This reduction is equal to $k$, the number of fundamental dimensions required to describe the variables of the physical problem in its original setting. This makes the approach ideal when the number of variables of the physical problem is not much greater than $k$. In this work, we demonstrate the effectiveness of the approach for the simple problem of the simultaneous estimation of the thickness and electrical conductivity of a conducting plate, via Eddy Current Testing. The approach is original, effective, efficient, and currently patent-pending. All the aspects, from theory to experimental validation, are provided, and it is proved that the proposed method achieves a very good accuracy over a wide range of thicknesses and electrical conductivities. Moreover, the proposed method is compatible with the in-line and real-time estimation of thickness and electrical conductivity in an industrial environment.