Basic restrictions for protecting against localized tissue heating induced from exposure to radiofrequency (RF) fields are typically specified as the specific energy absorption rate (SAR), which is mass averaged in recognition of the thermal diffusion properties of tissues. This article seeks to determine the most appropriate averaging mass (1, 3, 5, 7, or 10g) and averaging shape (cube or sphere). We also consider an alternative metric, volumetric energy absorption rate (VAR), which uses volume averaging (over 1, 3, 5, 7, and 10cm3; cube and sphere). The SAR and VAR averaging approaches were compared by considering which was a better predictor of tissue temperature rise (��T) induced by near- and far-field RF exposures (0.5-6GHz), calculated in a detailed human body model. For the exposure scenarios that we examined, VAR is better correlated with ��T than SAR, though not at a statistically significant level for most of the metric types we studied. However, as VAR offers substantive advantages in ease of assessment we recommend this metric over SAR. Averaging over a cube or a sphere provides equivalent levels of correlation with ��T, and so we recommend choosing the averaging shape on the basis of which is easier to assess. The optimal averaging volume is 10cm3 for VAR, and the optimal mass is 10g for SAR. The correlation between VAR or SAR and ��T diminishes substantially at 6GHz, where incident power flux density may be a better exposure metric. �� 2010 Wiley-Liss, Inc.