A method of evaluating the absorbed power density (APD) is studied to reconstruct the APD from fields measured outside the human body (phantom). It is based on the surface equivalence theorem and the Poggio–Miller–Chang–Harrington–Wu–Tsai (PMCHWT) formulation. The method is numerically studied and the issue related to the separation distance between the device under test (DUT) and the phantom is discussed. An accuracy improvement technique involving the suitable initialization of the iterative matrix solver is also presented.