An international interlaboratory comparison for numerical calculations of head phantom SAR involving three mobile phones with computer-aided design-based models has been conducted in order to evaluate the repeatability of such calculations and for providing input in the development of standardized procedures. SAR in the SAM head phantom was calculated by ten laboratories in a blind study manner. The agreement in the results ranged from good to poor and supports the opinion that standardized procedures for numerical calculations of SAR can be developed. Most likely a significant reason for the observed deviations is simplifications made to the models, which implies that device modeling specifications are of utmost importance in standards.