Herein, a comprehensive study of a large-sized (8 × 8 × 0.45 mm3) multisectoral boron-doped single-crystal diamond plate grown by high-pressure high-temperature method is presented. For the first time, electrochemical capacitance–voltage (ECV) technique is used to assess free charge carrier concentration in a single-crystal boron-doped diamond. Due to the absence of metal contacts and non-etching of diamond during electrochemical profiling, ECV measurements are performed in nondestructive mode, and the plate can be further used for device manufacturing. The registered free charge carrier concentration is on average 1 × 1016 cm−3 for the (100) growth sector and 1 × 1017 cm−3 for the (111) growth sector. The results obtained are further compared with Fourier-transform infrared spectroscopy evaluations of boron concentration. The adequate coincidence is found.