The purpose of this work was to investigate the dependence of whole-body averaged specific energy absorption rate (SAR), calculated using the finite-difference time-domain (FDTD) method, on the width of the free space region between a numerical phantom and the perfectly matched layer (pml) absorbing boundary. Results show that an increase in this width from 2 cells to 70 cells caused variations in the calculated whole-body averaged SAR of less than 2% for the FDTD code employing split-field pmls. Similarly, an increase in the width of the pml layer had little effect on the whole-body SAR values.