This paper discusses a method for improving sonic boom estimation in free-flight experiments. The multipole method can take into account the three-dimensional shock wave properties of consolidation while producing adequate data of a near-field pressure distribution required for sonic boom estimation. Although this multipole method is often used in the numerical simulations for sonic boom minimization, it has not been adapted experimentally yet. In this study, sonic boom estimation assisted by the multipole method is performed for two models using the results of computation fluid dynamics and the free-flight experiments. For an axisymmetric model, the multipole method estimates sonic boom accurately by comparing with the actual sonic boom from the field measurement. Further investigation is conducted with a non-axisymmetric wing body model to confirm the effectiveness of the multipole method.