Computed tomography (CT) is one of the diagnostic imaging exams that contributes to the largest dose in populations due to medical exposure in imaging. In this modality, optimization of doses is fundamental for radiological protection, especially in the case of pediatric patients. For diagnostic imaging reference levels (DRL), the dose descriptor Size - Specific Dose Estimates (SSDE) can be obtained from the computed tomography dose index (CTDI) by applying a factor estimated using the actual size of the patient: patient size-dependent factors. In this study, we employed the American Association of Physicists in Medicine (AAPM) methodology and directed measurements estimating patient size-dependent factors using different CT equipment and phantoms (6 years old pediatric anthropomorphic and polymethylmethacrylate phantoms), and we compared the results. Experimental data show that patient size-dependent factors are dependent on high-voltage tube and CT scan models, which have an important influence on SSDE values.