The present paper describes a finite difference time domain-based numerical approach to determine the dielectric properties of the tissue equivalent liquid employed in homogeneous phantoms when testing the specific absorption rate (SAR) compliance of mobile phones. A first numerical simulation performed with a realistic anatomical head model provides the reference averaged SAR value. Several similar simulations are then carried out using a homogeneous head model by varying the dielectric parameters of the tissue equivalent liquid. The desired dielectric parameters of the liquid are derived by matching the maximum averaged SAR with the reference value.