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 standardized specific anthropomorphic mannequin (SAM) head phantom was calculated by ten laboratories in a blind study manner. The agreement in calculated SAR between the participating laboratories is very similar to the agreement obtained in interlaboratory comparisons involving SAR measurements. The results support the opinion that standardized procedures for numerical calculations of SAR can be developed. The agreement between calculated SAR results and corresponding measurement results ranges from good to poor for the three phone models. Most probably, a significant reason for the observed deviations is the simplifications made to the models, which implies that device modeling specifications are of utmost importance in standards.