A method and device for calculating the Specific Absorption Rate (SAR) caused in a body by the electric field of a wireless communications device. The method involves using a model of a body, wherein the device is placed in proximity to the model and the electric field is measured at discrete points, including measuring the magnitude of the electric field at points of a first and a second surface of the model. By means of the measured magnitudes, the phase at said points is determined, such that the complex electric field at said points is determined. The complex electric field at said points is then used to determine the complex electric field in the model of the body. The complex electric field is used in order to calculate the SAR value caused by the device.