Non-destructive testing using ground-penetrating radar (GPR) allows the exploration of concrete structures up to several centimetres in depth and provides an indicative measurement of the size of the reinforcement bar (rebar). The large volume of raw data obtained from the GPR results in the analysis process being computationally expensive and more challenges are faced in the interpretation of the results. In the present work, a new method of thresholding is introduced to extract the hyperbolic pattern that occurs in the presence of the rebar. The peak of the extracted hyperbola is indicative of the location. Using the peak and start/end points of the hyperbola, the size of the rebar is estimated using a generalised method proposed in this paper. Furthermore, sample concrete blocks with both a single rod and three rods are used for the measurement and a commercial GPR unit, with a central frequency of 2600 MHz giving higher resolution, is used to obtain the data. The results obtained for the rebar by the proposed approach are compared with those obtained using methods reported in the literature.