In dermatology and in cosmetic science, the detailed analysis of the skin surface is still a key requirement to evaluate the effectiveness of medical or cosmetic treatments. Nowadays, the assessment of skin surface topographic structures such as wrinkles or micro-relief 3D profile is mainly obtained by profilometric analysis. Even though such an analysis gives a high level of detail, it is not suitable for in vivo studies since it requires the use of silicone cast replica of the skin. However, in the last few years a portable capacitive device has been proposed for in vivo skin topography characterization. This work presents the method we have developed to assess the capability of the capacitive device to provide reliable absolute measures of the skin surface structures. Extensive experiments carried out by comparing the measures achieved by means of the capacitive device and an optical profilometer allow us to validate our method.