Specific absorption rate (SAR) is a measure of the rate at which radio frequency (RF) electromagnetic energy is absorbed by the body when exposed to an RF field. It quantifies how much energy from RF devices, such as mobile phones, is deposited per unit of mass of biological tissue.

SAR is defined as the power absorbed per mass of tissue and has units of watts per kilogram (W/kg). It is usually averaged either over the whole body or over a small sample volume, typically 1 g or 10 g of tissue.

Government safety agencies have established SAR limits for RF exposure from electronic devices like cell phones and tablets, which primarily expose the head and limbs to RF energy during operation. Adherence to these SAR limits is meant to prevent excessive heating and other negative health effects in human tissue from RF energy absorption.